--- a/Cargo.lock
+++ b/Cargo.lock
@@ -264,23 +264,23 @@ dependencies = [
  "libc 0.2.43 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
 name = "bzip2-sys"
 version = "0.1.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "cc 1.0.18 (registry+https://github.com/rust-lang/crates.io-index)",
+ "cc 1.0.23 (registry+https://github.com/rust-lang/crates.io-index)",
  "libc 0.2.43 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
 name = "cc"
-version = "1.0.18"
+version = "1.0.23"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
 name = "cexpr"
 version = "0.2.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "nom 3.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -325,17 +325,17 @@ dependencies = [
  "vec_map 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
 name = "cmake"
 version = "0.1.29"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "cc 1.0.18 (registry+https://github.com/rust-lang/crates.io-index)",
+ "cc 1.0.23 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
 name = "cookie"
 version = "0.11.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "time 0.1.40 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1154,17 +1154,17 @@ name = "libc"
 version = "0.2.43"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
 name = "libloading"
 version = "0.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "cc 1.0.18 (registry+https://github.com/rust-lang/crates.io-index)",
+ "cc 1.0.23 (registry+https://github.com/rust-lang/crates.io-index)",
  "winapi 0.3.4 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
 name = "libudev"
 version = "0.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
@@ -1206,17 +1206,17 @@ dependencies = [
  "lmdb-sys 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
 name = "lmdb-sys"
 version = "0.8.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "cc 1.0.18 (registry+https://github.com/rust-lang/crates.io-index)",
+ "cc 1.0.23 (registry+https://github.com/rust-lang/crates.io-index)",
  "libc 0.2.43 (registry+https://github.com/rust-lang/crates.io-index)",
  "pkg-config 0.3.9 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
 name = "lock_api"
 version = "0.1.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -1312,17 +1312,17 @@ dependencies = [
  "libc 0.2.43 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
 name = "miniz_oxide_c_api"
 version = "0.1.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "cc 1.0.18 (registry+https://github.com/rust-lang/crates.io-index)",
+ "cc 1.0.23 (registry+https://github.com/rust-lang/crates.io-index)",
  "crc 1.7.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "libc 0.2.43 (registry+https://github.com/rust-lang/crates.io-index)",
  "miniz_oxide 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
 name = "mio"
 version = "0.6.15"
@@ -2849,17 +2849,17 @@ dependencies = [
 "checksum bitflags 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)" = "b3c30d3802dfb7281680d6285f2ccdaa8c2d8fee41f93805dba5c4cf50dc23cf"
 "checksum bitreader 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)" = "80b13e2ab064ff3aa0bdbf1eff533f9822dc37899821f5f98c67f263eab51707"
 "checksum boxfnonce 0.0.3 (registry+https://github.com/rust-lang/crates.io-index)" = "8380105befe91099e6f69206164072c05bc92427ff6aa8a5171388317346dd75"
 "checksum build_const 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "e90dc84f5e62d2ebe7676b83c22d33b6db8bd27340fb6ffbff0a364efa0cb9c9"
 "checksum byteorder 1.2.1 (registry+https://github.com/rust-lang/crates.io-index)" = "652805b7e73fada9d85e9a6682a4abd490cb52d96aeecc12e33a0de34dfd0d23"
 "checksum bytes 0.4.9 (registry+https://github.com/rust-lang/crates.io-index)" = "e178b8e0e239e844b083d5a0d4a156b2654e67f9f80144d48398fcd736a24fb8"
 "checksum bzip2 0.3.2 (registry+https://github.com/rust-lang/crates.io-index)" = "c3eafc42c44e0d827de6b1c131175098fe7fb53b8ce8a47e65cb3ea94688be24"
 "checksum bzip2-sys 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)" = "2c5162604199bbb17690ede847eaa6120a3f33d5ab4dcc8e7c25b16d849ae79b"
-"checksum cc 1.0.18 (registry+https://github.com/rust-lang/crates.io-index)" = "2119ea4867bd2b8ed3aecab467709720b2d55b1bcfe09f772fd68066eaf15275"
+"checksum cc 1.0.23 (registry+https://github.com/rust-lang/crates.io-index)" = "c37f0efaa4b9b001fa6f02d4b644dee4af97d3414df07c51e3e4f015f3a3e131"
 "checksum cexpr 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)" = "42aac45e9567d97474a834efdee3081b3c942b2205be932092f53354ce503d6c"
 "checksum cfg-if 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)" = "d4c819a1287eb618df47cc647173c5c4c66ba19d888a6e50d605672aed3140de"
 "checksum chrono 0.2.25 (registry+https://github.com/rust-lang/crates.io-index)" = "9213f7cd7c27e95c2b57c49f0e69b1ea65b27138da84a170133fd21b07659c00"
 "checksum clang-sys 0.23.0 (registry+https://github.com/rust-lang/crates.io-index)" = "d7f7c04e52c35222fffcc3a115b5daf5f7e2bfb71c13c4e2321afe1fc71859c2"
 "checksum clap 2.31.2 (registry+https://github.com/rust-lang/crates.io-index)" = "f0f16b89cbb9ee36d87483dc939fe9f1e13c05898d56d7b230a0d4dff033a536"
 "checksum cmake 0.1.29 (registry+https://github.com/rust-lang/crates.io-index)" = "56d741ea7a69e577f6d06b36b7dff4738f680593dc27a701ffa8506b73ce28bb"
 "checksum cookie 0.11.0 (registry+https://github.com/rust-lang/crates.io-index)" = "1465f8134efa296b4c19db34d909637cb2bf0f7aaf21299e23e18fa29ac557cf"
 "checksum core-foundation 0.6.0 (registry+https://github.com/rust-lang/crates.io-index)" = "c7caa6cb9e76ddddbea09a03266d6b3bc98cd41e9fb9b017c473e7cca593ec25"

--- a/third_party/rust/cc/.cargo-checksum.json
+++ b/third_party/rust/cc/.cargo-checksum.json
@@ -1,1 +1,1 @@
-{"files":{".travis.yml":"26bcb4e14726789c4bdf8783f445820c012d82d623ea51beb985d4d4ec870733","Cargo.toml":"b921b2f55193e3c4b09fa93329734c5811fb1e5a08c5fb6f10b960147403564d","LICENSE-APACHE":"a60eea817514531668d7e00765731449fe14d059d3249e0bc93b36de45f759f2","LICENSE-MIT":"378f5840b258e2779c39418f3f2d7b2ba96f1c7917dd6be0713f88305dbda397","README.md":"186c5c8a62520cb7a3d90d77161c954b52ae8456fca0e0669bc3a5b889592a43","appveyor.yml":"ab45bfdcf2596f357225a54e730c34d518a8f3ad56c2ed33af682cfd45bddc02","src/bin/gcc-shim.rs":"d6be9137cb48b86891e7b263adbf492e1193ffe682db9ba4a88eb1079b874b58","src/com.rs":"8b9a54af5400c259f877126cc68ea63ada4fe66e84c9b840711c95e570b15774","src/lib.rs":"f0b231d2e1923d43cd987278ccf4f20d55a6da4e2959061f57434d87428f003d","src/registry.rs":"3cc1b5a50879fa751572878ae1d0afbfc960c11665258492754b2c8bccb0ff5d","src/setup_config.rs":"f5c45afc99ad3b7c1311242bc4baf37e861d740ab81bf6ca90e2aa283672e65a","src/winapi.rs":"d7929b36130e33f1caa6bd444b378b83023b2b82d589c6e0ab38c4ff6c950da8","src/windows_registry.rs":"e31ce7a3273d67f99387edf28c5a9b4d6efab8f03fe446079c2b1ede6a21ffdb","tests/cc_env.rs":"bf7b14aa52af04294f648b2934f0f1830c5a0bdac1676310b8aa1f61458e7782","tests/support/mod.rs":"80dc87e54025197104cfb62d1af7a3400a3a0ddf0f2d98ea4ef4111cb1f0c890","tests/test.rs":"a6f4fde55631b0a8726cfb026791759c92720a5ba890e6989e9405d5acf461db"},"package":"2119ea4867bd2b8ed3aecab467709720b2d55b1bcfe09f772fd68066eaf15275"}
\ No newline at end of file
+{"files":{".travis.yml":"7b18272b20d4b58996deb3e2d5d76f15a27d6a63a061abeefb6553a2b8650736","Cargo.toml":"0e602ae4afdc3ef9f90fe332119cea84ee657465ab07fb106dc20d92acb3dff2","LICENSE-APACHE":"a60eea817514531668d7e00765731449fe14d059d3249e0bc93b36de45f759f2","LICENSE-MIT":"378f5840b258e2779c39418f3f2d7b2ba96f1c7917dd6be0713f88305dbda397","README.md":"3eeb4b0488908876c439a87cfe2bec6d550b37388993b2d8863fb1c587a84f46","appveyor.yml":"ab45bfdcf2596f357225a54e730c34d518a8f3ad56c2ed33af682cfd45bddc02","src/bin/gcc-shim.rs":"d6be9137cb48b86891e7b263adbf492e1193ffe682db9ba4a88eb1079b874b58","src/com.rs":"8b9a54af5400c259f877126cc68ea63ada4fe66e84c9b840711c95e570b15774","src/lib.rs":"2699109dc5b79829a026896f8401b54b78f90778734c4a5a34c772679dc48071","src/registry.rs":"3cc1b5a50879fa751572878ae1d0afbfc960c11665258492754b2c8bccb0ff5d","src/setup_config.rs":"f5c45afc99ad3b7c1311242bc4baf37e861d740ab81bf6ca90e2aa283672e65a","src/winapi.rs":"d7929b36130e33f1caa6bd444b378b83023b2b82d589c6e0ab38c4ff6c950da8","src/windows_registry.rs":"e31ce7a3273d67f99387edf28c5a9b4d6efab8f03fe446079c2b1ede6a21ffdb","tests/cc_env.rs":"bf7b14aa52af04294f648b2934f0f1830c5a0bdac1676310b8aa1f61458e7782","tests/support/mod.rs":"80dc87e54025197104cfb62d1af7a3400a3a0ddf0f2d98ea4ef4111cb1f0c890","tests/test.rs":"653b7d9ad6503aaf2ffc6c9b86014dbad456b53bcd124c9de4714067f49e5095"},"package":"c37f0efaa4b9b001fa6f02d4b644dee4af97d3414df07c51e3e4f015f3a3e131"}
\ No newline at end of file

--- a/third_party/rust/cc/.travis.yml
+++ b/third_party/rust/cc/.travis.yml
@@ -1,14 +1,14 @@
 language: rust
 sudo: false
 
 matrix:
   include:
-    - rust: 1.13.0
+    - rust: 1.16.0
       install:
       script: cargo build
     - rust: stable
       env: TARGET=x86_64-unknown-linux-gnu NO_ADD=1
     - rust: stable
       env: TARGET=i686-unknown-linux-gnu
     - os: osx
       env: TARGET=x86_64-apple-darwin NO_ADD=1
@@ -28,18 +28,27 @@ matrix:
       after_success:
         - travis-cargo --only nightly doc-upload
 
 install:
   - if [ -z "$NO_ADD" ]; then rustup target add $TARGET; fi
 
 script:
   - cargo build --verbose
-  - cargo test --verbose $NO_RUN
-  - cargo test --verbose --features parallel $NO_RUN
+  # FIXME: no idea why `--test-threads=1` is required on the OSX builder, it
+  # just randomly broke one day when the travis image was upgraded, and
+  # debugging turned up no easily found source of bugs...
+  #
+  # good build - https://travis-ci.org/alexcrichton/cc-rs/builds/409602374
+  #  bad build - https://travis-ci.org/alexcrichton/cc-rs/builds/410489079
+  #
+  # Those are using the same compiler, same commit, same... everything. Except
+  # the OSX image! No idea what changed...
+  - cargo test --verbose $NO_RUN -- --test-threads=1
+  - cargo test --verbose --features parallel $NO_RUN -- --test-threads=1
   - cargo test --manifest-path cc-test/Cargo.toml --target $TARGET $NO_RUN
   - cargo test --manifest-path cc-test/Cargo.toml --target $TARGET --features parallel $NO_RUN
   - cargo test --manifest-path cc-test/Cargo.toml --target $TARGET --release $NO_RUN
   - cargo doc
   - cargo clean && cargo build
   - rustdoc --test README.md -L target/debug -L target/debug/deps
 
 env:

--- a/third_party/rust/cc/Cargo.toml
+++ b/third_party/rust/cc/Cargo.toml
@@ -7,17 +7,17 @@
 #
 # If you believe there's an error in this file please file an
 # issue against the rust-lang/cargo repository. If you're
 # editing this file be aware that the upstream Cargo.toml
 # will likely look very different (and much more reasonable)
 
 [package]
 name = "cc"
-version = "1.0.18"
+version = "1.0.23"
 authors = ["Alex Crichton <alex@alexcrichton.com>"]
 description = "A build-time dependency for Cargo build scripts to assist in invoking the native\nC compiler to compile native C code into a static archive to be linked into Rust\ncode.\n"
 homepage = "https://github.com/alexcrichton/cc-rs"
 documentation = "https://docs.rs/cc"
 readme = "README.md"
 keywords = ["build-dependencies"]
 categories = ["development-tools"]
 license = "MIT/Apache-2.0"

--- a/third_party/rust/cc/README.md
+++ b/third_party/rust/cc/README.md
@@ -193,10 +193,10 @@ This project is licensed under either of
  * MIT license ([LICENSE-MIT](LICENSE-MIT) or
    http://opensource.org/licenses/MIT)
 
 at your option.
 
 ### Contribution
 
 Unless you explicitly state otherwise, any contribution intentionally submitted
-for inclusion in Serde by you, as defined in the Apache-2.0 license, shall be
+for inclusion in cc-rs by you, as defined in the Apache-2.0 license, shall be
 dual licensed as above, without any additional terms or conditions.

--- a/third_party/rust/cc/src/lib.rs
+++ b/third_party/rust/cc/src/lib.rs
@@ -111,18 +111,18 @@ pub struct Build {
     compiler: Option<PathBuf>,
     archiver: Option<PathBuf>,
     cargo_metadata: bool,
     pic: Option<bool>,
     static_crt: Option<bool>,
     shared_flag: Option<bool>,
     static_flag: Option<bool>,
     warnings_into_errors: bool,
-    warnings: bool,
-    extra_warnings: bool,
+    warnings: Option<bool>,
+    extra_warnings: Option<bool>,
 }
 
 /// Represents the types of errors that may occur while using cc-rs.
 #[derive(Clone, Debug)]
 enum ErrorKind {
     /// Error occurred while performing I/O.
     IOError,
     /// Invalid architecture supplied.
@@ -170,16 +170,17 @@ impl From<io::Error> for Error {
 pub struct Tool {
     path: PathBuf,
     cc_wrapper_path: Option<PathBuf>,
     cc_wrapper_args: Vec<OsString>,
     args: Vec<OsString>,
     env: Vec<(OsString, OsString)>,
     family: ToolFamily,
     cuda: bool,
+    removed_args: Vec<OsString>,
 }
 
 /// Represents the family of tools this tool belongs to.
 ///
 /// Each family of tools differs in how and what arguments they accept.
 ///
 /// Detection of a family is done on best-effort basis and may not accurately reflect the tool.
 #[derive(Copy, Clone, Debug, PartialEq)]
@@ -190,20 +191,25 @@ enum ToolFamily {
     /// and its cross-compilation approach is different.
     Clang,
     /// Tool is the MSVC cl.exe.
     Msvc { clang_cl: bool },
 }
 
 impl ToolFamily {
     /// What the flag to request debug info for this family of tools look like
-    fn debug_flag(&self) -> &'static str {
+    fn add_debug_flags(&self, cmd: &mut Tool) {
         match *self {
-            ToolFamily::Msvc { .. } => "/Z7",
-            ToolFamily::Gnu | ToolFamily::Clang => "-g",
+            ToolFamily::Msvc { .. } => {
+                cmd.push_cc_arg("/Z7".into());
+            }
+            ToolFamily::Gnu | ToolFamily::Clang => {
+                cmd.push_cc_arg("-g".into());
+                cmd.push_cc_arg("-fno-omit-frame-pointer".into());
+            }
         }
     }
 
     /// What the flag to include directories into header search path looks like
     fn include_flag(&self) -> &'static str {
         match *self {
             ToolFamily::Msvc { .. } => "/I",
             ToolFamily::Gnu | ToolFamily::Clang => "-I",
@@ -254,16 +260,20 @@ impl ToolFamily {
     /// NVCC-specific. Redirect the following flag to the underlying C++
     /// compiler.
     fn nvcc_redirect_flag(&self) -> &'static str {
         match *self {
             ToolFamily::Msvc { .. } => unimplemented!(),
             ToolFamily::Gnu | ToolFamily::Clang => "-Xcompiler",
         }
     }
+
+    fn verbose_stderr(&self) -> bool {
+        *self == ToolFamily::Clang
+    }
 }
 
 /// Represents an object.
 ///
 /// This is a source file -> object file pair.
 #[derive(Clone, Debug)]
 struct Object {
     src: PathBuf,
@@ -304,18 +314,18 @@ impl Build {
             opt_level: None,
             debug: None,
             env: Vec::new(),
             compiler: None,
             archiver: None,
             cargo_metadata: true,
             pic: None,
             static_crt: None,
-            warnings: true,
-            extra_warnings: true,
+            warnings: None,
+            extra_warnings: None,
             warnings_into_errors: false,
         }
     }
 
     /// Add a directory to the `-I` or include path for headers
     ///
     /// # Example
     ///
@@ -417,17 +427,24 @@ impl Build {
         let mut cfg = Build::new();
         cfg.flag(flag)
             .target(&target)
             .opt_level(0)
             .host(&host)
             .debug(false)
             .cpp(self.cpp)
             .cuda(self.cuda);
-        let compiler = cfg.try_get_compiler()?;
+        let mut compiler = cfg.try_get_compiler()?;
+
+        // Clang uses stderr for verbose output, which yields a false positive
+        // result if the CFLAGS/CXXFLAGS include -v to aid in debugging.
+        if compiler.family.verbose_stderr() {
+            compiler.remove_arg("-v".into());
+        }
+
         let mut cmd = compiler.to_command();
         let is_arm = target.contains("aarch64") || target.contains("arm");
         command_add_output_file(&mut cmd, &obj, target.contains("msvc"), false, is_arm);
 
         // We need to explicitly tell msvc not to link and create an exe
         // in the root directory of the crate
         if target.contains("msvc") {
             cmd.arg("/c");
@@ -575,18 +592,18 @@ impl Build {
     ///
     /// ```no_run
     /// cc::Build::new()
     ///     .file("src/foo.c")
     ///     .warnings(false)
     ///     .compile("libfoo.a");
     /// ```
     pub fn warnings(&mut self, warnings: bool) -> &mut Build {
-        self.warnings = warnings;
-        self.extra_warnings = warnings;
+        self.warnings = Some(warnings);
+        self.extra_warnings = Some(warnings);
         self
     }
 
     /// Set extra warnings flags.
     ///
     /// Adds some flags:
     /// - nothing for MSVC.
     /// - "-Wextra" for GNU and Clang.
@@ -598,17 +615,17 @@ impl Build {
     /// ```no_run
     /// // Disables -Wextra, -Wall remains enabled:
     /// cc::Build::new()
     ///     .file("src/foo.c")
     ///     .extra_warnings(false)
     ///     .compile("libfoo.a");
     /// ```
     pub fn extra_warnings(&mut self, warnings: bool) -> &mut Build {
-        self.extra_warnings = warnings;
+        self.extra_warnings = Some(warnings);
         self
     }
 
     /// Set the standard library to link against when compiling with C++
     /// support.
     ///
     /// The default value of this property depends on the current target: On
     /// OS X `Some("c++")` is used, when compiling for a Visual Studio based
@@ -1111,18 +1128,18 @@ impl Build {
             cmd.args.push(arg.into());
         }
 
         if self.get_debug() {
             if self.cuda {
                 let nvcc_debug_flag = cmd.family.nvcc_debug_flag().into();
                 cmd.args.push(nvcc_debug_flag);
             }
-            let debug_flag = cmd.family.debug_flag().into();
-            cmd.push_cc_arg(debug_flag);
+            let family = cmd.family;
+            family.add_debug_flags(&mut cmd);
         }
 
         // Target flags
         match cmd.family {
             ToolFamily::Clang => {
                 cmd.args.push(format!("--target={}", target).into());
             }
             ToolFamily::Msvc { clang_cl } => {
@@ -1240,16 +1257,41 @@ impl Build {
 
                     if target.ends_with("eabihf") {
                         cmd.args.push("-mfpu=fpv4-sp-d16".into())
                     }
                 }
                 if target.starts_with("thumbv7m") {
                     cmd.args.push("-march=armv7-m".into());
                 }
+                if target.starts_with("armebv7r") | target.starts_with("armv7r") {
+                    if target.starts_with("armeb") {
+                        cmd.args.push("-mbig-endian".into());
+                    } else {
+                        cmd.args.push("-mlittle-endian".into());
+                    }
+
+                    // ARM mode
+                    cmd.args.push("-marm".into());
+
+                    // R Profile
+                    cmd.args.push("-march=armv7-r".into());
+
+                    if target.ends_with("eabihf") {
+                        // Calling convention
+                        cmd.args.push("-mfloat-abi=hard".into());
+
+                        // lowest common denominator FPU
+                        // (see Cortex-R4 technical reference manual)
+                        cmd.args.push("-mfpu=vfpv3-d16".into())
+                    } else {
+                        // Calling convention
+                        cmd.args.push("-mfloat-abi=soft".into());
+                    }
+                }
             }
         }
 
         if target.contains("-ios") {
             // FIXME: potential bug. iOS is always compiled with Clang, but Gcc compiler may be
             // detected instead.
             self.ios_flags(&mut cmd)?;
         }
@@ -1277,22 +1319,27 @@ impl Build {
             }
         }
 
         for directory in self.include_directories.iter() {
             cmd.args.push(cmd.family.include_flag().into());
             cmd.args.push(directory.into());
         }
 
-        if self.warnings {
+        // If warnings and/or extra_warnings haven't been explicitly set,
+        // then we set them only if the environment doesn't already have
+        // CFLAGS/CXXFLAGS, since those variables presumably already contain
+        // the desired set of warnings flags.
+
+        if self.warnings.unwrap_or(if self.has_flags() { false } else { true }) {
             let wflags = cmd.family.warnings_flags().into();
             cmd.push_cc_arg(wflags);
         }
 
-        if self.extra_warnings {
+        if self.extra_warnings.unwrap_or(if self.has_flags() { false } else { true }) {
             if let Some(wflags) = cmd.family.extra_warnings_flags() {
                 cmd.push_cc_arg(wflags.into());
             }
         }
 
         for flag in self.flags.iter() {
             cmd.args.push(flag.into());
         }
@@ -1319,16 +1366,22 @@ impl Build {
         if self.warnings_into_errors {
             let warnings_to_errors_flag = cmd.family.warnings_to_errors_flag().into();
             cmd.push_cc_arg(warnings_to_errors_flag);
         }
 
         Ok(cmd)
     }
 
+    fn has_flags(&self) -> bool {
+        let flags_env_var_name = if self.cpp { "CXXFLAGS" } else { "CFLAGS" };
+        let flags_env_var_value = self.get_var(flags_env_var_name);
+        if let Ok(_) = flags_env_var_value { true } else { false }
+    }
+
     fn msvc_macro_assembler(&self) -> Result<(Command, String), Error> {
         let target = self.get_target()?;
         let tool = if target.contains("x86_64") {
             "ml64.exe"
         } else if target.contains("arm") {
             "armasm.exe"
         } else if target.contains("aarch64") {
             "armasm64.exe"
@@ -1532,20 +1585,20 @@ impl Build {
     }
 
     fn get_base_compiler(&self) -> Result<Tool, Error> {
         if let Some(ref c) = self.compiler {
             return Ok(Tool::new(c.clone()));
         }
         let host = self.get_host()?;
         let target = self.get_target()?;
-        let (env, msvc, gnu, traditional) = if self.cpp {
-            ("CXX", "cl.exe", "g++", "c++")
+        let (env, msvc, gnu, traditional, clang) = if self.cpp {
+            ("CXX", "cl.exe", "g++", "c++", "clang++")
         } else {
-            ("CC", "cl.exe", "gcc", "cc")
+            ("CC", "cl.exe", "gcc", "cc", "clang")
         };
 
         // On Solaris, c++/cc unlikely to exist or be correct.
         let default = if host.contains("solaris") {
             gnu
         } else {
             traditional
         };
@@ -1590,34 +1643,40 @@ impl Build {
             None => {
                 let compiler = if host.contains("windows") && target.contains("windows") {
                     if target.contains("msvc") {
                         msvc.to_string()
                     } else {
                         format!("{}.exe", gnu)
                     }
                 } else if target.contains("android") {
-                    format!(
-                        "{}-{}",
-                        target
-                            .replace("armv7", "arm")
-                            .replace("armv7neon", "arm")
-                            .replace("thumbv7", "arm")
-                            .replace("thumbv7neon", "arm"),
-                        gnu
-                    )
+                    let target = target
+                        .replace("armv7", "arm")
+                        .replace("armv7neon", "arm")
+                        .replace("thumbv7", "arm")
+                        .replace("thumbv7neon", "arm");
+                    let gnu_compiler = format!("{}-{}", target, gnu);
+                    let clang_compiler = format!("{}-{}", target, clang);
+                    // Check if gnu compiler is present
+                    // if not, use clang
+                    if Command::new(&gnu_compiler).spawn().is_ok() {
+                        gnu_compiler
+                    } else {
+                        clang_compiler
+                    }
                 } else if target.contains("cloudabi") {
                     format!("{}-{}", target, traditional)
                 } else if self.get_host()? != target {
                     // CROSS_COMPILE is of the form: "arm-linux-gnueabi-"
                     let cc_env = self.getenv("CROSS_COMPILE");
                     let cross_compile = cc_env.as_ref().map(|s| s.trim_right_matches('-'));
                     let prefix = cross_compile.or(match &target[..] {
                         "aarch64-unknown-linux-gnu" => Some("aarch64-linux-gnu"),
                         "aarch64-unknown-linux-musl" => Some("aarch64-linux-musl"),
+                        "aarch64-unknown-netbsd" => Some("aarch64--netbsd"),
                         "arm-unknown-linux-gnueabi" => Some("arm-linux-gnueabi"),
                         "armv4t-unknown-linux-gnueabi" => Some("arm-linux-gnueabi"),
                         "armv5te-unknown-linux-gnueabi" => Some("arm-linux-gnueabi"),
                         "arm-frc-linux-gnueabi" => Some("arm-frc-linux-gnueabi"),
                         "arm-unknown-linux-gnueabihf" => Some("arm-linux-gnueabihf"),
                         "arm-unknown-linux-musleabi" => Some("arm-linux-musleabi"),
                         "arm-unknown-linux-musleabihf" => Some("arm-linux-musleabihf"),
                         "arm-unknown-netbsd-eabi" => Some("arm--netbsdelf-eabi"),
@@ -1644,16 +1703,20 @@ impl Build {
                         "powerpc-unknown-netbsd" => Some("powerpc--netbsd"),
                         "powerpc64-unknown-linux-gnu" => Some("powerpc-linux-gnu"),
                         "powerpc64le-unknown-linux-gnu" => Some("powerpc64le-linux-gnu"),
                         "s390x-unknown-linux-gnu" => Some("s390x-linux-gnu"),
                         "sparc-unknown-linux-gnu" => Some("sparc-linux-gnu"),
                         "sparc64-unknown-linux-gnu" => Some("sparc64-linux-gnu"),
                         "sparc64-unknown-netbsd" => Some("sparc64--netbsd"),
                         "sparcv9-sun-solaris" => Some("sparcv9-sun-solaris"),
+                        "armebv7r-none-eabi" => Some("arm-none-eabi"),
+                        "armebv7r-none-eabihf" => Some("arm-none-eabi"),
+                        "armv7r-none-eabi" => Some("arm-none-eabi"),
+                        "armv7r-none-eabihf" => Some("arm-none-eabi"),
                         "thumbv6m-none-eabi" => Some("arm-none-eabi"),
                         "thumbv7em-none-eabi" => Some("arm-none-eabi"),
                         "thumbv7em-none-eabihf" => Some("arm-none-eabi"),
                         "thumbv7m-none-eabi" => Some("arm-none-eabi"),
                         "x86_64-pc-windows-gnu" => Some("x86_64-w64-mingw32"),
                         "x86_64-rumprun-netbsd" => Some("x86_64-rumprun-netbsd"),
                         "x86_64-unknown-linux-musl" => Some("musl"),
                         "x86_64-unknown-netbsd" => Some("x86_64--netbsd"),
@@ -1954,19 +2017,25 @@ impl Tool {
         Tool {
             path: path,
             cc_wrapper_path: None,
             cc_wrapper_args: Vec::new(),
             args: Vec::new(),
             env: Vec::new(),
             family: family,
             cuda: cuda,
+            removed_args: Vec::new(),
         }
     }
 
+    /// Add an argument to be stripped from the final command arguments.
+    fn remove_arg(&mut self, flag: OsString) {
+        self.removed_args.push(flag);
+    }
+
     /// Add a flag, and optionally prepend the NVCC wrapper flag "-Xcompiler".
     ///
     /// Currently this is only used for compiling CUDA sources, since NVCC only
     /// accepts a limited set of GNU-like flags, and the rest must be prefixed
     /// with a "-Xcompiler" flag to get passed to the underlying C++ compiler.
     fn push_cc_arg(&mut self, flag: OsString) {
         if self.cuda {
             self.args.push(self.family.nvcc_redirect_flag().into());
@@ -1984,17 +2053,20 @@ impl Tool {
             Some(ref cc_wrapper_path) => {
                 let mut cmd = Command::new(&cc_wrapper_path);
                 cmd.arg(&self.path);
                 cmd
             }
             None => Command::new(&self.path),
         };
         cmd.args(&self.cc_wrapper_args);
-        cmd.args(&self.args);
+
+        let value = self.args.iter().filter(|a| !self.removed_args.contains(a)).collect::<Vec<_>>();
+        cmd.args(&value);
+
         for &(ref k, ref v) in self.env.iter() {
             cmd.env(k, v);
         }
         cmd
     }
 
     /// Returns the path for this compiler.
     ///

--- a/third_party/rust/cc/tests/test.rs
+++ b/third_party/rust/cc/tests/test.rs
@@ -1,11 +1,12 @@
 extern crate cc;
 extern crate tempdir;
 
+use std::env;
 use support::Test;
 
 mod support;
 
 #[test]
 fn gnu_smoke() {
     let test = Test::gnu();
     test.gcc().file("foo.c").compile("foo");
@@ -106,16 +107,40 @@ fn gnu_warnings_overridable() {
         .file("foo.c")
         .compile("foo");
 
     test.cmd(0)
         .must_have_in_order("-Wall", "-Wno-missing-field-initializers");
 }
 
 #[test]
+fn gnu_no_warnings_if_cflags() {
+    env::set_var("CFLAGS", "-Wflag-does-not-exist");
+    let test = Test::gnu();
+    test.gcc()
+        .file("foo.c")
+        .compile("foo");
+
+    test.cmd(0).must_not_have("-Wall").must_not_have("-Wextra");
+    env::set_var("CFLAGS", "");
+}
+
+#[test]
+fn gnu_no_warnings_if_cxxflags() {
+    env::set_var("CXXFLAGS", "-Wflag-does-not-exist");
+    let test = Test::gnu();
+    test.gcc()
+        .file("foo.c")
+        .compile("foo");
+
+    test.cmd(0).must_not_have("-Wall").must_not_have("-Wextra");
+    env::set_var("CXXFLAGS", "");
+}
+
+#[test]
 fn gnu_x86_64() {
     for vendor in &["unknown-linux-gnu", "apple-darwin"] {
         let target = format!("x86_64-{}", vendor);
         let test = Test::gnu();
         test.gcc()
             .target(&target)
             .host(&target)
             .file("foo.c")
@@ -225,22 +250,24 @@ fn gnu_shared() {
 #[test]
 fn gnu_flag_if_supported() {
     if cfg!(windows) {
         return;
     }
     let test = Test::gnu();
     test.gcc()
         .file("foo.c")
+        .flag("-v")
         .flag_if_supported("-Wall")
         .flag_if_supported("-Wflag-does-not-exist")
         .flag_if_supported("-std=c++11")
         .compile("foo");
 
     test.cmd(0)
+        .must_have("-v")
         .must_have("-Wall")
         .must_not_have("-Wflag-does-not-exist")
         .must_not_have("-std=c++11");
 }
 
 #[test]
 fn gnu_flag_if_supported_cpp() {
     if cfg!(windows) {