[clang][deps] Handle modular dependencies present in PCH
When a translation unit uses a PCH and imports the same modules as the PCH, we'd prefer to resolve to those modules instead of inventing new modules and reporting them as modular dependencies. Since the PCH modules have already been built nudge the compiler to reuse them when deciding whether to build a new module and don't report them as regular modular dependencies.
Reviewed By: dexonsmith
Differential Revision: https://reviews.llvm.org/D103526