[Frontend] Make WrapperFrontendAction call WrappedAction.PrepareToExecuteAction.

[vsapsai]

Summary

Fixes -emit-header-module when GenerateHeaderModuleAction is wrapped
by another frontend action.

rdar://problem/47302588

[arphaman]

That LGTM.

[vsapsai]

Thanks for the review.

clang/include/clang/Frontend/FrontendAction.h

 ///
 /// Deriving from this class allows an action to inject custom logic around
 /// some existing action's behavior. It implements every virtual method in
 /// the FrontendAction interface by forwarding to the wrapped action.
 class WrapperFrontendAction : public FrontendAction {
   std::unique_ptr<FrontendAction> WrappedAction;
 
 protected:
+  bool PrepareToExecuteAction(CompilerInstance &CI) override;
   std::unique_ptr<ASTConsumer> CreateASTConsumer(CompilerInstance &CI,
                                                  StringRef InFile) override;
   bool BeginInvocation(CompilerInstance &CI) override;
   bool BeginSourceFileAction(CompilerInstance &CI) override;
   void ExecuteAction() override;
   void EndSourceFileAction() override;
 
 public:

clang/lib/Frontend/FrontendAction.cpp

 void PluginASTAction::anchor() { }
 
 std::unique_ptr<ASTConsumer>
 PreprocessorFrontendAction::CreateASTConsumer(CompilerInstance &CI,
                                               StringRef InFile) {
   llvm_unreachable("Invalid CreateASTConsumer on preprocessor action!");
 }
 
+bool WrapperFrontendAction::PrepareToExecuteAction(CompilerInstance &CI) {
+  return WrappedAction->PrepareToExecuteAction(CI);
+}
 std::unique_ptr<ASTConsumer>
 WrapperFrontendAction::CreateASTConsumer(CompilerInstance &CI,
                                          StringRef InFile) {
   return WrappedAction->CreateASTConsumer(CI, InFile);
 }
 bool WrapperFrontendAction::BeginInvocation(CompilerInstance &CI) {
   return WrappedAction->BeginInvocation(CI);
 }