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

[Aaron Puchert via cfe-commits]

aaronpuchert wrote:

Doesn't this fit better in `Sema/SemaDeclAttr.cpp`? That's where we're checking the attributes themselves and whether they make sense on a declaration. This would seem like a good place to check against previous declarations. Though to be fair, I don't know how late the late-parsed attributes are parsed, is that really at the end of the file?

The analysis in `Analysis/ThreadSafety.cpp` is based on the CFG of a function definition and at least so far doesn't really care about multiple declarations. But if it's the only way to make it work I guess we'll have to bite the bullet.

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