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

[Michael Park via cfe-commits]

mpark wrote:

> > But if we want relocatable modules without using `-fmodules-embed-all-files` though, is there a solution for that?
> 
> Do you use `-no-canonical-prefixes`?

Hi Richard! Hm, no we do not. I haven't seen this before. I can try it though 🤔

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