Random temporary string cleanup.

llvm-svn: 110807
diff --git a/clang/lib/Lex/Lexer.cpp b/clang/lib/Lex/Lexer.cpp
index b492d77..7e6f7c1 100644
--- a/clang/lib/Lex/Lexer.cpp
+++ b/clang/lib/Lex/Lexer.cpp
@@ -671,7 +671,7 @@
   }
 
   if (!L->isLexingRawMode())
-    L->Diag(CP-2, diag::trigraph_converted) << std::string()+Res;
+    L->Diag(CP-2, diag::trigraph_converted) << llvm::StringRef(&Res, 1);
   return Res;
 }