Use twines to simplify calls to report_fatal_error. For code size and readability.

llvm-svn: 100756
diff --git a/llvm/lib/CodeGen/ELFWriter.cpp b/llvm/lib/CodeGen/ELFWriter.cpp
index 651e7e9..fe55b32 100644
--- a/llvm/lib/CodeGen/ELFWriter.cpp
+++ b/llvm/lib/CodeGen/ELFWriter.cpp
@@ -572,10 +572,8 @@
   }
   }
 
-  std::string msg(CE->getOpcodeName());
-  raw_string_ostream ErrorMsg(msg);
-  ErrorMsg << ": Unsupported ConstantExpr type";
-  report_fatal_error(ErrorMsg.str());
+  report_fatal_error(CE->getOpcodeName() +
+                     StringRef(": Unsupported ConstantExpr type"));
 
   return std::make_pair(CV, 0); // silence warning
 }