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

[Sam McCall via cfe-commits]

sam-mccall wrote:

#89441 fixes our build problems, with or without this patch applied.

It's possible this patch makes things better - I haven't checked for actual sloc usage yet, just whether the build fails.

So I'll focus on understanding that one and then return here.

(I think I'm close to a sharable reproducer too)

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