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

[James Y Knight via cfe-commits]

jyknight wrote:

It seems to me that we could simplify the implementation by being a bit more literal in the interpretation of the requirements: look only at the type, alignment, name, and bitfield-width of members. Just don't bother checking other stuff

I'd hope it can look more like a simple loop over the fields of the two record types (similar to mergeFunctionTypes's checks of the functions' param types), rather than starting with the very-complex ASTStructuralEquivalence.cpp, and adding even more complexity to validate attributes.

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