[clang] [Clang]Throw frontend error for target feature mismatch when using `flatten` attribute (PR #150044)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

Also, the changes should come with a release note to `clang/docs/ReleaseNotes.rst` so users know about the fix.

https://github.com/llvm/llvm-project/pull/150044