[clang] [clang] WIP: Warn on mismatched RequiresCapability attributes (PR #67520)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> @AaronBallman Is the prototype of the implementation here at least sound? Or should this go somewhere completely different? Maybe in one of the TSA source files?

This is a semantic concern rather than a syntactic one, so I would expect this to happen in Sema rather than in Parser. My intuition is that this would be most natural in `mergeDeclAttributes()` as that's where this sort of thing typically lives for non-late parsed attributes. We merge the attributes when merging function declarations, so perhaps we need to add `mergeLateParsedDeclAttributes()` for ones that require late parsing?

CC @erichkeane in case he has opinions.


https://github.com/llvm/llvm-project/pull/67520