[clang] [Clang] Implement P3034R1 Module Declarations Shouldn’t be Macros (PR #90574)

[Matheus Izvekov via cfe-commits]

mizvekov wrote:

> It would be nice to have a reproducer. I can't tell the root cause from this error, so I can't use it to strengthen the current tests.

I intend to provide a reproducer. I just can't do it today. So don't wait on it as a justification to avoid reverting.

https://github.com/llvm/llvm-project/pull/90574