Bug 1730078 - Build clang-tidy with clang. r=firefox-build-system-reviewers,andi

There are complications with building a 1-stage clang with gcc, so just
use clang. Eventually, the clang-tidy toolchains will be removed in
favor of providing clang-tidy from the clang toolchain itself anyways.

Differential Revision: https://phabricator.services.mozilla.com/D125158

build/build-clang/clang-tidy-external-linux64.json

@@ -4,9 +4,9 @@
     "build_type": "Release",
     "assertions": false,
     "build_clang_tidy": true,
-    "cc": "{MOZ_FETCHES_DIR}/gcc/bin/gcc",
-    "cxx": "{MOZ_FETCHES_DIR}/gcc/bin/g++",
-    "as": "{MOZ_FETCHES_DIR}/gcc/bin/gcc",
+    "cc": "{MOZ_FETCHES_DIR}/clang/bin/clang",
+    "cxx": "{MOZ_FETCHES_DIR}/clang/bin/clang++",
+    "as": "{MOZ_FETCHES_DIR}/clang/bin/clang",
     "patches": [
         "clang-tidy-ci.patch"
     ],

build/build-clang/clang-tidy-linux64.json

@@ -4,9 +4,9 @@
     "build_type": "Release",
     "assertions": false,
     "build_clang_tidy": true,
-    "cc": "{MOZ_FETCHES_DIR}/gcc/bin/gcc",
-    "cxx": "{MOZ_FETCHES_DIR}/gcc/bin/g++",
-    "as": "{MOZ_FETCHES_DIR}/gcc/bin/gcc",
+    "cc": "{MOZ_FETCHES_DIR}/clang/bin/clang",
+    "cxx": "{MOZ_FETCHES_DIR}/clang/bin/clang++",
+    "as": "{MOZ_FETCHES_DIR}/clang/bin/clang",
     "patches": [
         "clang-tidy-ci.patch"
     ]

taskcluster/ci/toolchain/clang-tidy.yml

@@ -40,8 +40,7 @@ linux64-clang-tidy:
         - trunk
     fetches:
         toolchain:
-            - linux64-binutils
-            - linux64-gcc-7
+            - linux64-clang-12
             - linux64-toolchain-sysroot
 
 macosx64-clang-tidy:
@@ -60,10 +59,8 @@ macosx64-clang-tidy:
         - trunk
     fetches:
         toolchain:
-            - linux64-binutils
             - linux64-cctools-port-clang-12
             - linux64-clang-12-macosx-cross
-            - linux64-gcc-7
             - macosx64-sdk-10.12
 
 macosx64-arch64-clang-tidy:
@@ -85,10 +82,8 @@ macosx64-arch64-clang-tidy:
         - trunk
     fetches:
         toolchain:
-            - linux64-binutils
             - linux64-cctools-port-clang-12
             - linux64-clang-12-macosx-cross
-            - linux64-gcc-7
             - macosx64-sdk-11.0
 
 win64-clang-tidy:
@@ -141,6 +136,5 @@ linux64-clang-tidy-external:
         fetch:
             - civet-source
         toolchain:
-            - linux64-binutils
-            - linux64-gcc-7
+            - linux64-clang-12
             - linux64-toolchain-sysroot