[clang][modules][deps] System module maps might not be affecting

The dependency scanner relies on the module map filtering logic in `ASTWriter`. The algorithm currently considers all system module maps affecting, which is not only sub-optimal, but can also cause failures when building a module explicitly (see attached test case).

This patch applies the same filtering logic to system module maps.

Reviewed By: Bigcheese

Differential Revision: https://reviews.llvm.org/D136007