The a2ps ebuild doesn't have an "emacs" USE flag and misses emacs in its dependencies. Emacs is auto-detected by the package's build system. Furthermore, it could profit from a site-init file to properly enable a2ps support in Emacs. Patches will follow.
Created attachment 138508 [details, diff] Proposed changes for a2ps-4.13c-r5.ebuild
Created attachment 138510 [details] Emacs site-init file, goes to files/50a2ps-gentoo.el
Created attachment 138520 [details] Emacs site-init file, goes to files/50a2ps-gentoo.el Removed redundant .* in auto-mode regexp.
Fixed.