gdm-3.5.91-r1 lacks gdm-launch-environment.pam which cause it to fail to start.
Seems gdm-welcome should be renamed to gdm-launch-environment https://mail.gnome.org/archives/commits-list/2012-August/msg00231.html
Thanks, should be fixed in gdm-3.5.91-r2. > commit 93a2b16ae5c56a1a089d90fe508abfedcc1e8a26 > Author: Alexandre Rostovtsev <tetromino@gentoo.org> > Date: Fri Sep 14 15:04:46 2012 -0400 > > gnome-base/gdm: use pam.d/gdm-launch-environment (bug #434966) > > Thanks to Maciej Piechotka and Peter Sääf.