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

[Timm Baeder via cfe-commits]

tbaederr 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?

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