cmGlobalVisualStudioGenerator: Simplify __create_def command generation

Source/cmGlobalVisualStudioGenerator.cxx

@@ -843,9 +843,8 @@ void cmGlobalVisualStudioGenerator::AddSymbolExportCommand(
   std::string obj_dir_expanded = obj_dir;
   cmSystemTools::ReplaceString(obj_dir_expanded, this->GetCMakeCFGIntDir(),
                                configName.c_str());
-  std::string objs_file = obj_dir_expanded;
-  cmSystemTools::MakeDirectory(objs_file.c_str());
-  objs_file += "/objects.txt";
+  cmSystemTools::MakeDirectory(obj_dir_expanded);
+  std::string const objs_file = obj_dir_expanded + "/objects.txt";
   cmdl.push_back(objs_file);
   cmGeneratedFileStream fout(objs_file.c_str());
   if (!fout) {