[clang] [clang][modules] Track Included Files Per Submodule (PR #170215)

[Ian Anderson via cfe-commits]

ian-twilightcoder wrote:

I am a bit worried that this change will make it so that multiple modules will "absorb" non-modular headers, which will result in incompatible types in Swift. On the other hand, having one random module absorb the non-modular header isn't _really_ much better...

https://github.com/llvm/llvm-project/pull/170215