Bug 1736459 - Switch the spidermonkey fuzzing build to clang 13. r=firefox-build-system-reviewers,andi

It was waiting for rust 1.56. Consequently remove clang 12, since it's
not used anymore.

Differential Revision: https://phabricator.services.mozilla.com/D129322

taskcluster/ci/fetch/toolchains.yml

@@ -373,13 +373,6 @@ clang-10:
         repo: https://github.com/llvm/llvm-project
         revision: d32170dbd5b0d54436537b6b75beaf44324e0c28
 
-clang-12:
-    description: clang 12.0.1 source code
-    fetch:
-        type: git
-        repo: https://github.com/llvm/llvm-project
-        revision: fed41342a82f5a3a9201819a82bf7a48313e296b
-
 clang-13:
     description: clang 13.0.0 source code
     fetch:

taskcluster/ci/spidermonkey/linux.yml

@@ -430,9 +430,7 @@ sm-fuzzing-linux64/opt:
         spidermonkey-variant: fuzzing
     fetches:
         toolchain:
-            # Keep this with clang-12 until we move to rust 1.56 that uses the same
-            # LLVM-13 backend as clang-13
-            - linux64-clang-12
+            - linux64-clang-13
             - linux64-rust
             - linux64-cbindgen
             - linux64-dump_syms

taskcluster/ci/toolchain/clang.yml

@@ -130,27 +130,6 @@ linux64-clang-trunk:
             - linux64-toolchain-sysroot
             - wasm32-wasi-compiler-rt
 
-linux64-clang-12:
-    description: "Clang 12 toolchain build"
-    attributes:
-        local-toolchain: true
-    treeherder:
-        symbol: TL(clang12)
-    run-on-projects: [trunk]
-    run:
-        using: toolchain-script
-        script: build-clang.sh
-        arguments:
-            - 'build/build-clang/clang-12-linux64.json'
-        resources:
-            - 'build/build-clang/clang-12-linux64.json'
-        toolchain-artifact: public/build/clang.tar.zst
-    fetches:
-        fetch:
-            - clang-12
-        toolchain:
-            - linux64-toolchain-sysroot
-
 linux64-clang-13:
     description: "Clang 13 toolchain build"
     attributes: