[clang] [clang][DependencyScanning] Track modules that resolve from sysroot. (PR #130634)

[Ben Langmuir via cfe-commits]

https://github.com/benlangmuir commented:

I have a similar concern to @jansvoboda11 that we probably need to check the invocation paths as well.  

> I would think that if ModuleDepCollector only found dependency inputs that resolve to sysroot locations, the command line for building the specific module wouldn't matter.

One concern I have is if we have user search paths, the contents of those paths can change after scanning in a way that silently affects the compilation. Another more theoretical issue is that in general the set of module input files has no guarantee of being complete -- it's derived from the source manager and we don't necessarily have a mechanism to ensure every file that impacted the module was captured.

https://github.com/llvm/llvm-project/pull/130634