Bug 1508547 - Switch Android builds to clang 7 again. r=dmajor

Bug 1492663 upgraded those builds to clang 7, and bug 1503330 brought
them back to clang 6 because of speedometer regressions.

With the previous change, the regression doesn't happen any more,
allowing to upgrade again.

Depends on D12394

Differential Revision: https://phabricator.services.mozilla.com/D12395

--HG--
extra : moz-landing-system : lando

build/build-clang/clang-6-linux64.json

@@ -1,26 +0,0 @@
-{
-    "llvm_revision": "335538",
-    "stages": "3",
-    "build_libcxx": true,
-    "build_type": "Release",
-    "assertions": false,
-    "llvm_repo": "https://llvm.org/svn/llvm-project/llvm/tags/RELEASE_601/final",
-    "clang_repo": "https://llvm.org/svn/llvm-project/cfe/tags/RELEASE_601/final",
-    "lld_repo": "https://llvm.org/svn/llvm-project/lld/tags/RELEASE_601/final",
-    "compiler_repo": "https://llvm.org/svn/llvm-project/compiler-rt/tags/RELEASE_601/final",
-    "libcxx_repo": "https://llvm.org/svn/llvm-project/libcxx/tags/RELEASE_601/final",
-    "libcxxabi_repo": "https://llvm.org/svn/llvm-project/libcxxabi/tags/RELEASE_601/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": [
-      "static-llvm-symbolizer.patch",
-      "find_symbolizer_linux.patch",
-      "r322325.patch",
-      "r322401.patch",
-      "r325356.patch",
-      "r339636.patch"
-    ]
-}

taskcluster/ci/build/android.yml

@@ -340,7 +340,7 @@ android-api-16/opt:
         - android-gradle-dependencies
         - android-ndk-linux
         - android-sdk-linux
-        - linux64-clang-6
+        - linux64-clang
         - linux64-rust-android
         - linux64-rust-size
         - linux64-cbindgen
@@ -394,7 +394,7 @@ android-api-16-without-google-play-services/opt:
         - android-gradle-dependencies
         - android-ndk-linux
         - android-sdk-linux
-        - linux64-clang-6
+        - linux64-clang
         - linux64-rust-android
         - linux64-rust-size
         - linux64-cbindgen
@@ -456,7 +456,7 @@ android-api-16-nightly/opt:
         - android-gradle-dependencies
         - android-ndk-linux
         - android-sdk-linux
-        - linux64-clang-6
+        - linux64-clang
         - linux64-rust-android
         - linux64-rust-size
         - linux64-cbindgen
@@ -513,7 +513,7 @@ android-aarch64/opt:
         - android-gradle-dependencies
         - android-ndk-linux
         - android-sdk-linux
-        - linux64-clang-6
+        - linux64-clang
         - linux64-rust-android
         - linux64-rust-size
         - linux64-cbindgen
@@ -575,7 +575,7 @@ android-aarch64-nightly/opt:
         - android-gradle-dependencies
         - android-ndk-linux
         - android-sdk-linux
-        - linux64-clang-6
+        - linux64-clang
         - linux64-rust-android
         - linux64-rust-size
         - linux64-sccache

taskcluster/ci/toolchain/linux.yml

@@ -27,27 +27,6 @@ linux64-clang-3.9:
     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
-    worker:
-        max-run-time: 7200
-    run:
-        using: toolchain-script
-        script: build-clang-6-linux.sh
-        resources:
-            - 'build/build-clang/build-clang.py'
-            - 'build/build-clang/clang-6-linux64.json'
-            - 'taskcluster/scripts/misc/tooltool-download.sh'
-        toolchain-artifact: public/build/clang.tar.xz
-    toolchains:
-        - linux64-gcc-4.9
-
 linux64-clang-7:
     description: "Clang 7 toolchain build"
     treeherder:

taskcluster/scripts/misc/build-clang-6-linux.sh

@@ -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-6-linux64.json
-
-set -x
-
-# Put a tarball in the artifacts dir
-mkdir -p $UPLOAD_DIR
-cp clang.tar.* $UPLOAD_DIR