[llvm] [clang] [clang][DependencyScanner] Remove unused -ivfsoverlay files (PR #73734)

[Jan Svoboda via cfe-commits]

jansvoboda11 wrote:

I'm not thrilled by the chosen implementation strategy. Disabling tracking during parts of header search does not sound obviously correct to me. Module map search can have subtle side-effects, and I wouldn't be suprised if this feature was affected by one. That said, I haven't been able to come up with a case where this would yield incorrect results.

An alternative implementation I'd be more confident in would be to grab the set of files we know affect the compilation (built on top of `ASTWriter::collectNonAffectingInputFiles()`) and call `FileManager::getOptionalFileRef()` with their `FileEntryRef::getNameAsRequested()`.

https://github.com/llvm/llvm-project/pull/73734