>>> Compiling source in /var/tmp/portage/nas-1.7-r1/work/nas-1.7 ... /usr/portage/media-libs/nas/nas-1.7-r1.ebuild: line 42: xmkmf: command not found That about says it all :)
it's apparently imake that provides that program
imake is in the deps for nas-1.7-r1.ebuild