[clang][NFC] Preprocessor only needs const LangOptions (llvm#66874)

Author: tbaederr

clang/include/clang/Lex/Preprocessor.h

@@ -132,7 +132,7 @@ class Preprocessor {
   llvm::unique_function<void(const clang::Token &)> OnToken;
   std::shared_ptr<PreprocessorOptions> PPOpts;
   DiagnosticsEngine        *Diags;
-  LangOptions       &LangOpts;
+  const LangOptions &LangOpts;
   const TargetInfo *Target = nullptr;
   const TargetInfo *AuxTarget = nullptr;
   FileManager       &FileMgr;
@@ -1161,8 +1161,9 @@ class Preprocessor {
 
 public:
   Preprocessor(std::shared_ptr<PreprocessorOptions> PPOpts,
-               DiagnosticsEngine &diags, LangOptions &opts, SourceManager &SM,
-               HeaderSearch &Headers, ModuleLoader &TheModuleLoader,
+               DiagnosticsEngine &diags, const LangOptions &LangOpts,
+               SourceManager &SM, HeaderSearch &Headers,
+               ModuleLoader &TheModuleLoader,
                IdentifierInfoLookup *IILookup = nullptr,
                bool OwnsHeaderSearch = false,
                TranslationUnitKind TUKind = TU_Complete);

clang/lib/Lex/Preprocessor.cpp

@@ -77,7 +77,7 @@ LLVM_INSTANTIATE_REGISTRY(PragmaHandlerRegistry)
 ExternalPreprocessorSource::~ExternalPreprocessorSource() = default;
 
 Preprocessor::Preprocessor(std::shared_ptr<PreprocessorOptions> PPOpts,
-                           DiagnosticsEngine &diags, LangOptions &opts,
+                           DiagnosticsEngine &diags, const LangOptions &opts,
                            SourceManager &SM, HeaderSearch &Headers,
                            ModuleLoader &TheModuleLoader,
                            IdentifierInfoLookup *IILookup, bool OwnsHeaders,