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

[via cfe-commits]

kjedruczyk wrote:

Thanks, @cor3ntin - all checks are green now. I imagine I don't need to rebase the branch on the current main as there are no conflicts that I can see, and rebasing would probably clear the CI checks.

If the workflow allows it, please merge it at your convenience!

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