[clang] [AMDGPU] Diagnose unaligned atomic (PR #80322)

[Artem Belevich via cfe-commits]

https://github.com/Artem-B approved this pull request.

You may want to check that we can still disable the error with `-Wno-error=atomic-alignment` passed via top-level options.

Other than that LGTM.

https://github.com/llvm/llvm-project/pull/80322