[clang] [C++20] [Modules] Don't check redeclaration for TagUseKind::Referencekind declaration (PR #194546)

[Matheus Izvekov via cfe-commits]

https://github.com/mizvekov commented:

I think this is a compiler bug, but the fix doesn't look right.

I don't think the line `struct kevent evt;` should have introduced a new declaration of `kevent`, because this refers to an entity which has already been declared before, so I don't think this should have fallen into the "declared in elaboration" case.

https://github.com/llvm/llvm-project/pull/194546