for library_dir in configuration.get('library_dirs', []):
        if library_dir not in xcode_standard_library_dirs and (
            not xcbc.HasBuildSetting(_library_search_paths_var) or
            library_dir not in xcbc.GetBuildSetting(_library_search_paths_var)):
          xcbc.AppendBuildSetting(_library_search_paths_var, library_dir)