[clang][serialization] Reduce ASTWriter::writeUnhashedControlBlock() scope

(cherry picked from commit 304c412)

Author: jansvoboda11

clang/include/clang/Serialization/ASTWriter.h

@@ -543,7 +543,7 @@ class ASTWriter : public ASTDeserializationListener,
   void WriteControlBlock(Preprocessor &PP, StringRef isysroot);
 
   /// Write out the signature and diagnostic options, and return the signature.
-  void writeUnhashedControlBlock(Preprocessor &PP, ASTContext &Context);
+  void writeUnhashedControlBlock(Preprocessor &PP);
   ASTFileSignature backpatchSignature();
 
   /// Calculate hash of the pcm content.

clang/lib/Serialization/ASTWriter.cpp

@@ -1264,8 +1264,7 @@ ASTFileSignature ASTWriter::backpatchSignature() {
   return Signature;
 }
 
-void ASTWriter::writeUnhashedControlBlock(Preprocessor &PP,
-                                          ASTContext &Context) {
+void ASTWriter::writeUnhashedControlBlock(Preprocessor &PP) {
   using namespace llvm;
 
   // Flush first to prepare the PCM hash (signature).
@@ -1318,7 +1317,7 @@ void ASTWriter::writeUnhashedControlBlock(Preprocessor &PP,
   const auto &HSOpts = PP.getHeaderSearchInfo().getHeaderSearchOpts();
 
   // Diagnostic options.
-  const auto &Diags = Context.getDiagnostics();
+  const auto &Diags = PP.getDiagnostics();
   const DiagnosticOptions &DiagOpts = Diags.getDiagnosticOptions();
   if (!HSOpts.ModulesSkipDiagnosticOptions) {
 #define DIAGOPT(Name, Bits, Default) Record.push_back(DiagOpts.Name);
@@ -5355,7 +5354,7 @@ ASTFileSignature ASTWriter::WriteASTCore(Sema &SemaRef, StringRef isysroot,
   // SourceLocations or FileIDs depends on it.
   computeNonAffectingInputFiles();
 
-  writeUnhashedControlBlock(PP, Context);
+  writeUnhashedControlBlock(PP);
 
   // Don't reuse type ID and Identifier ID from readers for C++ standard named
   // modules since we want to support no-transitive-change model for named