[clang] [C23] Implement WG14 N3037 (PR #132939)

[Martin Uecker via cfe-commits]

uecker wrote:

> 
> Once that is settled, then go back to work on redeclaration/definition support. Possibly it'd be good to pause and ask the standards body to clarify how it's supposed to work first. While I think my proposed semantics above make sense, the standard doesn't actually _specify_ that, one way or the other. And it should.

For  standard attributes, the standard explicitly makes it clear that redeclarations w/ and w/o attributes are ok and can be mixed. This is also what GCC implements. I do not think there is anything unclear in the standard. Each attribute has specific wording that clarifies this.


https://github.com/llvm/llvm-project/pull/132939