[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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@@ -276,6 +291,14 @@ class ModuleFile {
   /// The time is specified in seconds since the start of the Epoch.
   uint64_t InputFilesValidationTimestamp = 0;
 
+  /// Captures the high-level result of validating input files.
+  ///
+  /// Useful when encounter an invalid input file. This way can check what kind
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cyndyishida wrote:

nit: 
```suggestion
  /// Useful when encountering an invalid input file. This way, we can check what kind
```

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