From trying to ebuild kde-base/artsplugin-audiofile: checking for mcopidl... not found configure: error: The important program mcopidl was not found! Please check whether you installed aRts correctly or use --without-arts to compile without aRts support (this will remove functionality).
The check in the ebuild is incorrect, will break compile if you have USE="arts" but kdelibs was compiled with USE="-arts".
Been fixed over a months ago, closing.