Backed out changeset 7fbe19a6f88e (bug 1365601) as requested by bobowen for c3 failures. r=backout

Backed out changeset 6035f7b2a12c (bug 1365601)

Bug 1378440 - part 2 - add `mach cargo check`; r=rillian Cargo recently introduced the `cargo check` command for shortening the edit-compile cycle when working on large programs. Since we don't really support invoking `cargo` directly, let's wire up this command to `mach`. Gecko developers can then `mach cargo check` to ensure their changes typecheck.

Bug 1378440 - part 1 - make Cargo invocation macro more generic; r=rillian All the machinery we set up for `cargo build` is equally useful for other commands, such as `cargo check`. Let's refactor things so that it's easy to reuse said machinery for `cargo check`.

Bug 1376135 - Upgrade debugger frontend v0.7.0 (6/24). r=jdescottes

Bug 1377971 - part 3 - honor LIB_IS_C_ONLY in more cases; r=glandium We currently only honor LIB_IS_C_ONLY for cases where we set a LIBRARY (and, implicitly, REAL_LIBRARY) and FORCE_SHARED_LIB. For many libraries, such as the libraries from NSS, we never set LIBRARY, which leads to not setting REAL_LIBRARY, which leads to not honoring LIB_IS_C_ONLY. This practice has not been harmful thus far (except perhaps linking in more things than necessary to our NSS shared libraries), but on some platforms, linking with the C++ compiler will drag in more things than we would like. Consulting LIBRARY first should not be necessary; checking FORCE_SHARED_LIB should be enough to tell us if we're building a shared library for the purposes of honoring LIB_IS_C_ONLY.

Bug 1377971 - part 2 - link libavutil and libavcodec with libm; r=rillian Both of these libraries call into libm for various reasons, but by linking with the C++ compiler on most platforms, they never had to declare their dependency on libm. Future changes will make these libraries link with the C compiler, which won't automatically link with libm, so we need to make the dependency explicit prior to that change.

Bug 1377971 - part 1 - make C++ linking for Linkable ignore shared libraries; r=glandium We have a flag set on all Linkables, cxx_link, denoting whether there's anything being linked into them that requires C++. We do this even when we link against shared libraries that required C++. But if these libraries don't export C++ interfaces, there's no reason that the things linking against them should require C++. Therefore, ignore shared libraries when making the determination of whether an object requires C++ or not.

Bug 1310852 - part 4 - always download packages for stylo during `mach bootstrap`; r=rillian With configure now being able to auto-detect the presence of a `mach bootstrap`-installed clang and libclang and the upcoming build-by-defaultness of Stylo, we can start downloading these packages all the time.

Bug 1310852 - part 3 - don't install clang packages through tooltool for OS X `mach bootstrap`; r=rillian We decided to install the necessary packages through the appropriate Mac package manager instead.

Bug 1310852 - part 2 - search for Homebrew and MacPorts's llvm-config when appropriate; r=rillian Since Homebrew doesn't automatically place clang and associated binaries on PATH, we need to do the task ourselves. MacPorts does place the binaries in PATH, but uses yet another name, so we have to add that to the search list.

Bug 1310852 - part 1 - install llvm homebrew/macports packages; r=rillian LLVM/clang is needed for Stylo's bindgen, and Apple's clang is unusable for such purposes. For other platforms, we have installed LLVM/clang from our tooltool archive on the supposition that those packages are definitely known to work, as we use said packages in automation. For Mac, however, we haven't been able to generate packages for tooltool that successfully build Stylo, and even if we had, those packages would solely be used for developer builds of Stylo and would not be used in automation. The case for downloading LLVM/clang for Mac from tooltool, therefore, is not as strong as for other platforms. As a result, we'll rely on the installed package manager for LLVM/clang, which many people may have installed anyway. In passing, also delete some old code for OS X versions < 10.7; such platforms are no longer supported for running or building Firefox.

Bug 1377340 - NETWORK_RACE_CACHE_WITH_NETWORK_USAGE should separate delayed and non-delayed racing. r=valentin

Bug 1378252 - Add funsize routes to mac repackage-signing tasks r=Callek MozReview-Commit-ID: CzmGNqY18ic

Bug 1315092 - Part 2: Correctly clear mPrivateBrowsingId during the assertion as well on a CLOSED TREE, a=bustage MozReview-Commit-ID: J8j4DWUzl8D

Bug 1377299 - Part 1: (WIP) Add packet dump hooks MozReview-Commit-ID: Jr7n49OOduG

Bug 1378523 - Enable -fsanitize=trace-pc-guard for WebRTC in fuzzing. r?drno MozReview-Commit-ID: 9Fr9bwD3RAq

Bug 1377053 - Add test for discrete interpolation of stroke-dasharray with 'none'; r?hiro MozReview-Commit-ID: MuxvAeVwes

Bug 1377053 - Update test expectations based in fixed interpolation fallback behavior; r?hiro MozReview-Commit-ID: LcHuXa3dTpZ

Bug 1377053 - Crash test for interpolating zero-length lists in add_weighted; r=hiro MozReview-Commit-ID: DJJlKNZ4GKD