[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:

The only error is in CodeGen/PowerPC/subreg-lanemasks.mir and doesn't look related to this change.

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