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

[Matheus Izvekov via cfe-commits]

mizvekov wrote:

I am also seeing breakages which are solved by reverting this change.

The failure occurs when importing modules from within header files:

```
error: expected a module name after 'import'
   11 | import std;
```

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