[clang] [Clang] Reject __annotation on unsupported targets (PR #193731)

[via cfe-commits]

kjedruczyk wrote:

@efriedma-quic  - should we retry the run? If it helps I can rebase the branch on top of main, but AFAIK the CI runs on merged commit anyway.

> Still sanitizer_common/TestCases/Linux/pthread_join.cpp:72:17 relies n UB. If it happens frequently, we need to de-flake it.

If that helps, I can try to reproduce it on some arm64 SOC I have laying around, but I'm not sure I can reproduce exact environment the CI workflow uses.

https://github.com/llvm/llvm-project/pull/193731