[clang] [modules] Add diagnostic about performed input file validation when encounter unrecoverable changed input file. (PR #180899)

[Cyndy Ishida via cfe-commits]

cyndyishida wrote:

Silly question, if this error was emitted in a module that was compiled in the same compiler instance, what version of the note would we see? 
`input file validation has covered all files`? Should that be a special case?

https://github.com/llvm/llvm-project/pull/180899