GCStrategy: Use Twine properly for error message

Avoid unnecessary std::string temporaries.

Author: arsenm

llvm/lib/IR/GCStrategy.cpp

@@ -41,10 +41,9 @@ std::unique_ptr<GCStrategy> llvm::getGCStrategy(const StringRef Name) {
     // be the builtin GCs if nothing else.  The most likely scenario here is
     // that we got here without running the initializers used by the Registry
     // itself and it's registration mechanism.
-    const std::string error =
-        std::string("unsupported GC: ") + Name.str() +
-        " (did you remember to link and initialize the library?)";
-    report_fatal_error(Twine(error));
+    report_fatal_error(
+        "unsupported GC: " + Name +
+        " (did you remember to link and initialize the library?)");
   } else
-    report_fatal_error(Twine(std::string("unsupported GC: ") + Name.str()));
+    report_fatal_error(Twine("unsupported GC: ") + Name);
 }