[clang] [clang][Modules] Adding Specific Diagnostics when a Finalized PCM is Out-of-date due to Input File Changes (PR #209857)

[Jan Svoboda via cfe-commits]

jansvoboda11 wrote:

I guess one can think of this as a compiler bug caused by the in-memory module cache and the importee's `FileManager` disagreeing with the importer's `FileManager` on what the input file should look like.

https://github.com/llvm/llvm-project/pull/209857