[clang] Support '-fmodule-file-home-is-cwd' for C++ modules. (PR #135147)

[Michael Park via cfe-commits]

mpark wrote:

Going back to the idea of not writing the paths of imported PCMs at all; currently the condition to not write the paths is if the imported PCM is a named module. Perhaps this condition can be extended to omit the paths if the PCM was found through `-fmodule-file=<name>=<pcm>`? 

https://github.com/llvm/llvm-project/pull/135147