[clang] [clang][modules] HeaderSearch::MarkFileModuleHeader sets textual headers' HeaderFileInfo non-external when it shouldn't (PR #89005)

[Ian Anderson via cfe-commits]

ian-twilightcoder wrote:

>From Jan:

> Maybe we can add the number of external HeaderFileInfos to HeaderSearch::PrintStats() and have a test that checks for it.
> The flag to enable that output is -show-stats I think.

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