Fixes and closes llvm#53952

The issue llvm#53952 is reported indicating clang is giving a crashing pch file, when hasErrors is been passed incorrectly to WriteAST method.

To fix the issue, I have a added an assertion to make sure the given value of ASTHasCompilerErrors is matching with Preprocessor diagnostics. And this assertion will get triggered inside Debug builds.

For release builds, based on the conditional check, forcefully set the ASTHasCompilerErrors member variable to a valid value from Preprocessor.

Author: rajkumarananthu

clang/lib/Serialization/ASTWriter.cpp

@@ -4628,6 +4628,12 @@ ASTFileSignature ASTWriter::WriteAST(Sema &SemaRef, StringRef OutputFile,
   WritingAST = true;
 
   ASTHasCompilerErrors = hasErrors;
+  bool trueHasErrors = SemaRef.PP.getDiagnostics().hasUncompilableErrorOccurred();
+  assert(ASTHasCompilerErrors == trueHasErrors);
+  if (trueHasErrors != ASTHasCompilerErrors) {
+      // forcing the compiler errors flag to be set correctly
+      ASTHasCompilerErrors = trueHasErrors;
+  }
 
   // Emit the file header.
   Stream.Emit((unsigned)'C', 8);