/usr/lib/swi-prolog/xpce.rc is in swi-prolog-x 7.2.3-2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/swi-prolog/xpce/pl/xpce.rc
/usr/lib/swi-prolog/xpce/pl/xpce.rc