I've found that spim-7.3 emerges ok, but when running xspim it exits immediatly with an error related with exceptions.s. To correct it do as follows: edit /usr/portage/app-emulation/spim/spim-7.3.ebuild and change line 60 to: -e "s:\(EXCEPTION_DIR = \).*$:\1/var/lib/spim:" \ then ebuild spim-7.3.ebuild digest and reemerge spim.
Ah, didnt even notice that I had done that. That is the correct fix. Applied change in portage.