Revert "Adapt to LLVM optimization remark interface change. NFC"

This reverts commit r282500.

llvm-svn: 282504
diff --git a/clang/lib/CodeGen/CodeGenAction.cpp b/clang/lib/CodeGen/CodeGenAction.cpp
index f79ca7f..6a3b9c6 100644
--- a/clang/lib/CodeGen/CodeGenAction.cpp
+++ b/clang/lib/CodeGen/CodeGenAction.cpp
@@ -514,7 +514,7 @@
 
   std::string Msg;
   raw_string_ostream MsgStream(Msg);
-  MsgStream << D.getMsg();
+  MsgStream << D.getMsg().str();
 
   if (D.getHotness())
     MsgStream << " (hotness: " << *D.getHotness() << ")";