For multilib, EXTRA_MULTILIB_PARTS are used to build libgcc_s.so. I don't think it should be there at all.
Confirmed, patch here: <http://gcc.gnu.org/ml/gcc-patches/2004-11/msg01454.html>.
It looks like it has been fixed by http://gcc.gnu.org/ml/gcc-patches/2004-11/msg02707.html