Fix getCustomDiagID() usage in example code

This was setting a bad example. DiagIDs are a limited resource and the message
argument is evaluated as a format string.

llvm-svn: 197855

clang/examples/PrintFunctionNames/PrintFunctionNames.cpp

@@ -48,9 +48,9 @@ protected:
       // Example error handling.
       if (args[i] == "-an-error") {
         DiagnosticsEngine &D = CI.getDiagnostics();
-        unsigned DiagID = D.getCustomDiagID(
-          DiagnosticsEngine::Error, "invalid argument '" + args[i] + "'");
-        D.Report(DiagID);
+        unsigned DiagID = D.getCustomDiagID(DiagnosticsEngine::Error,
+                                            "invalid argument '%0'");
+        D.Report(DiagID) << args[i];
         return false;
       }
     }