Reduce the number of implicit StringRef->std::string conversions by threading StringRef through more APIs.

No functionality change intended.

llvm-svn: 260815
diff --git a/clang/lib/CodeGen/CGObjCGNU.cpp b/clang/lib/CodeGen/CGObjCGNU.cpp
index 2ca0f1a..bbe1b8b 100644
--- a/clang/lib/CodeGen/CGObjCGNU.cpp
+++ b/clang/lib/CodeGen/CGObjCGNU.cpp
@@ -591,7 +591,7 @@
     return NULLPtr;
   }
 
-  llvm::GlobalVariable *GetClassGlobal(const std::string &Name,
+  llvm::GlobalVariable *GetClassGlobal(StringRef Name,
                                        bool Weak = false) override {
     return nullptr;
   }