Refactor to remove the assumption that we know the name of the module we're emitting at the point when we create a PCHGenerator (with the C++ modules TS, we find that out part way through parsing the input).

llvm-svn: 279766
diff --git a/clang/lib/Frontend/ChainedIncludesSource.cpp b/clang/lib/Frontend/ChainedIncludesSource.cpp
index 7687b24..c5b77ee 100644
--- a/clang/lib/Frontend/ChainedIncludesSource.cpp
+++ b/clang/lib/Frontend/ChainedIncludesSource.cpp
@@ -161,7 +161,7 @@
     auto Buffer = std::make_shared<PCHBuffer>();
     ArrayRef<llvm::IntrusiveRefCntPtr<ModuleFileExtension>> Extensions;
     auto consumer = llvm::make_unique<PCHGenerator>(
-        Clang->getPreprocessor(), "-", nullptr, /*isysroot=*/"", Buffer,
+        Clang->getPreprocessor(), "-", /*isysroot=*/"", Buffer,
         Extensions, /*AllowASTWithErrors=*/true);
     Clang->getASTContext().setASTMutationListener(
                                             consumer->GetASTMutationListener());