[clang] [Modules] Add -cc1 -flate-module-map-file to load module maps after PCMs (PR #88893)

[Ilya Biryukov via cfe-commits]

ilya-biryukov wrote:

The comments on this thread bugged me, so I managed to find a way to achieve the same effect without adding any new flags. #112015 should give the deduplication that I want to get here without introducing any new flags, through a tweak to the mechanism of non-affecting source locations.

I will close this PR, let's continue discussion in #112015.

https://github.com/llvm/llvm-project/pull/88893