[clang] clang: Stop assuming one toolchain covers all GPUArchs (PR #190369)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `arc-builder` running on `arc-worker` while building `clang` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/3/builds/30912

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 6 (test-build-unified-tree-check-all) failure: 1200 seconds without output running [b'ninja', b'check-all'], attempting to kill
...
993.613 [1/11/60] Linking CXX executable unittests/Target/TargetMachineCTests
993.763 [1/10/61] Linking CXX executable unittests/IR/IRTests
993.977 [1/9/62] Linking CXX executable unittests/Transforms/Instrumentation/InstrumentationTests
994.008 [1/8/63] Linking CXX executable unittests/Transforms/Coroutines/CoroTests
994.187 [1/7/64] Linking CXX executable unittests/Passes/PassBuilderBindings/PassesBindingsTests
994.494 [1/6/65] Linking CXX executable unittests/Passes/Plugins/PluginsTests
994.727 [1/5/66] Linking CXX executable unittests/Transforms/Utils/UtilsTests
995.411 [1/4/67] Linking CXX executable unittests/Target/X86/X86Tests
995.488 [1/3/68] Linking CXX executable unittests/Transforms/Scalar/ScalarTests
996.073 [1/2/69] Linking CXX executable unittests/tools/llvm-mca/LLVMMCATests
command timed out: 1200 seconds without output running [b'ninja', b'check-all'], attempting to kill
process killed by signal 9
program finished with exit code -1
elapsedTime=2197.006398

```

</details>

https://github.com/llvm/llvm-project/pull/190369