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

[Cyndy Ishida via cfe-commits]

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@@ -3000,6 +3000,8 @@ InputFile ASTReader::getInputFile(ModuleFile &F, unsigned ID, bool Complain) {
       }
 
       Diag(diag::note_ast_file_rebuild_required) << TopLevelASTFileName;
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cyndyishida wrote:

Could this note only be emitted in the `Disabled` case? 
I also prefer changing the message a bit to something you suggested earlier, using passive voice, `please rebuild precompiled file` to `precompiled file needs to be rebuilt`. 

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