[clang] [clang][modules] Separate parsing of modulemaps (PR #119740)

[Michael Spencer via cfe-commits]

Bigcheese wrote:

> I'm happy with the way this split of the code worked out!
> 
> > Currently this has no effect other than slightly changing diagnostics.
> 
> Can you say more about the ordering changes? I understand we can't always emit diagnostics in source order, but it's helpful for readability when we do so I wasn't thrilled to see that seems to be changing.

Syntax diagnostics happen first, and then semantics. Like if a header file can't be found. As this is made more lazy the distance (in diagnostic order) between these will get larger, but that's largely unavoidable.

https://github.com/llvm/llvm-project/pull/119740