deleted file mode 100644
--- a/build/build-clang/clang-5-linux64.json
+++ /dev/null
@@ -1,22 +0,0 @@
-{
-    "llvm_revision": "320874",
-    "stages": "3",
-    "build_libcxx": true,
-    "build_type": "Release",
-    "assertions": false,
-    "llvm_repo": "https://llvm.org/svn/llvm-project/llvm/tags/RELEASE_501/final",
-    "clang_repo": "https://llvm.org/svn/llvm-project/cfe/tags/RELEASE_501/final",
-    "compiler_repo": "https://llvm.org/svn/llvm-project/compiler-rt/tags/RELEASE_501/final",
-    "libcxx_repo": "https://llvm.org/svn/llvm-project/libcxx/tags/RELEASE_501/final",
-    "libcxxabi_repo": "https://llvm.org/svn/llvm-project/libcxxabi/tags/RELEASE_501/final",
-    "python_path": "/usr/bin/python2.7",
-    "gcc_dir": "/builds/worker/workspace/build/src/gcc",
-    "cc": "/builds/worker/workspace/build/src/gcc/bin/gcc",
-    "cxx": "/builds/worker/workspace/build/src/gcc/bin/g++",
-    "as": "/builds/worker/workspace/build/src/gcc/bin/gcc",
-    "patches": [
-      "llvm-debug-frame-for-5.patch",
-      "r313872.patch",
-      "pr_set_ptracer.patch"
-    ]
-}

deleted file mode 100644
--- a/build/build-clang/pr_set_ptracer.patch
+++ /dev/null
@@ -1,27 +0,0 @@
---- a/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cc
-+++ b/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cc
-@@ -57,6 +57,14 @@
- #include "sanitizer_mutex.h"
- #include "sanitizer_placement_new.h"
- 
-+// Sufficiently old kernel headers don't provide this value, but we can still
-+// call prctl with it. If the runtime kernel is new enough, the prctl call will
-+// have the desired effect; if the kernel is too old, the call will error and we
-+// can ignore said error.
-+#ifndef PR_SET_PTRACER
-+#define PR_SET_PTRACER 0x59616d61
-+#endif
-+
- // This module works by spawning a Linux task which then attaches to every
- // thread in the caller process with ptrace. This suspends the threads, and
- // PTRACE_GETREGS can then be used to obtain their register state. The callback
-@@ -433,9 +441,7 @@
-     ScopedSetTracerPID scoped_set_tracer_pid(tracer_pid);
-     // On some systems we have to explicitly declare that we want to be traced
-     // by the tracer thread.
--#ifdef PR_SET_PTRACER
-     internal_prctl(PR_SET_PTRACER, tracer_pid, 0, 0, 0);
--#endif
-     // Allow the tracer thread to start.
-     tracer_thread_argument.mutex.Unlock();
-     // NOTE: errno is shared between this thread and the tracer thread.

--- a/taskcluster/ci/toolchain/linux.yml
+++ b/taskcluster/ci/toolchain/linux.yml
@@ -22,37 +22,16 @@ linux64-clang-3.9:
         resources:
             - 'build/build-clang/build-clang.py'
             - 'build/build-clang/clang-3.9-linux64.json'
             - 'taskcluster/scripts/misc/tooltool-download.sh'
         toolchain-artifact: public/build/clang.tar.xz
     toolchains:
         - linux64-gcc-4.9
 
-linux64-clang-5:
-    description: "Clang 5 toolchain build"
-    treeherder:
-        kind: build
-        platform: toolchains/opt
-        symbol: TL(clang5)
-        tier: 1
-    worker-type: aws-provisioner-v1/gecko-{level}-b-linux-xlarge
-    worker:
-        max-run-time: 7200
-    run:
-        using: toolchain-script
-        script: build-clang-5-linux.sh
-        resources:
-            - 'build/build-clang/build-clang.py'
-            - 'build/build-clang/clang-5-linux64.json'
-            - 'taskcluster/scripts/misc/tooltool-download.sh'
-        toolchain-artifact: public/build/clang.tar.xz
-    toolchains:
-        - linux64-gcc-4.9
-
 linux64-clang-6:
     description: "Clang 6 toolchain build"
     treeherder:
         kind: build
         platform: toolchains/opt
         symbol: TL(clang6)
         tier: 1
     worker-type: aws-provisioner-v1/gecko-{level}-b-linux-xlarge

deleted file mode 100755
--- a/taskcluster/scripts/misc/build-clang-5-linux.sh
+++ /dev/null
@@ -1,25 +0,0 @@
-#!/bin/bash
-set -x -e -v
-
-# This script is for building clang for Linux.
-
-WORKSPACE=$HOME/workspace
-HOME_DIR=$WORKSPACE/build
-UPLOAD_DIR=$HOME/artifacts
-
-cd $HOME_DIR/src
-
-. taskcluster/scripts/misc/tooltool-download.sh
-
-# gets a bit too verbose here
-set +x
-
-cd build/build-clang
-# |mach python| sets up a virtualenv for us!
-../../mach python ./build-clang.py -c clang-5-linux64.json
-
-set -x
-
-# Put a tarball in the artifacts dir
-mkdir -p $UPLOAD_DIR
-cp clang.tar.* $UPLOAD_DIR