[clang] [Clang] Make `-Xarch_` handling generic for all toolchains (PR #125421)

[Artem Belevich via cfe-commits]

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+// RUN: %clang -x cuda %s -Xarch_nvptx64 -O3 -S -nogpulib -nogpuinc -### 2>&1 | FileCheck -check-prefix=O3ONCE %s
+// RUN: %clang -x hip %s -Xarch_amdgcn -O3 -S -nogpulib -nogpuinc -### 2>&1 | FileCheck -check-prefix=O3ONCE %s
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Artem-B wrote:

> We have existing tests for those

We have a few scattered across hip-options.hip and openmp-offload-gpu.c and it would make sense to consolidate them here, now that we have the tests dedicated specifically to Xarch processing. 

https://github.com/llvm/llvm-project/pull/125421