[clang] [llvm] [clang][deps] Track directory dependencies of modules (PR #222202)

[Michael Spencer via llvm-commits]

Bigcheese wrote:

> Can you clarify what use-case does this capability serve?
> 
> > * letting the build system report which directories have been invalidated on
> >   future incremental builds.

This allows invalidating those modules during scanning. Just reporting is enough for the build system to invalidate the explicit builds, but this is needed to also invalidate the scanning PCMs.

https://github.com/llvm/llvm-project/pull/222202