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

[Volodymyr Sapsai via cfe-commits]

vsapsai wrote:

> Sorry, I have a lot of bike shedding comments, but thank you for adding this, Volodymyr!

No problem. Bike shedding comments are annoying if you are building a power plant. When you are repainting a bike shed  – they are welcome. And this PR doesn't look like building a power plant.

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