[clang] [clang][modules] HeaderSearch::MarkFileModuleHeader creates extra HeaderFileInfo, breaks PCM reuse (PR #89005)

[Ian Anderson via cfe-commits]

ian-twilightcoder wrote:

> As a test, maybe you could probe the resulting PCM with `-module-file-info`.

What would I be looking for? Presumably the problem is we import the same module twice but fail to find the built pcm in the module cache and so we build it again? I don't know what else would cause runaway growth of pcm files... I actually don't really understand the problem Ilya is hitting... But Richard found (2 now!) good bugs in my code and I'm hoping fixing that will fix Ilya's problem.

https://github.com/llvm/llvm-project/pull/89005