[clang] [AMDGPU] Do not emit arch dependent macros with unspecified cpu (PR #80035)

[Joseph Huber via cfe-commits]

jhuber6 wrote:

> This seems to break tests: http://45.33.8.238/linux/129493/step_7.txt
> 
> Please take a look and revert for now if it takes a while to fix.

Is it still broken? I pushed a fix because I'm pretty sure the problem was not passing `-nogpulib` `-nogpuinc` so the test runs on machines without ROCm. I always forget about that part because I have ROCm on my machine. It used to work silently before a patch last year or something that made `clang` failing make the test fail.

https://github.com/llvm/llvm-project/pull/80035