"guix-emacs.el" may be used just for "instructing" Emacs where to find
Emacs packages installed with Guix, so it should have as few
dependencies as possible.
See <http://lists.gnu.org/archive/html/guix-devel/2016-01/msg00022.html>.
* emacs/guix-emacs.el: Require 'guix-profiles' optionally.
(guix-emacs-load-autoloads): Use 'guix-profile-prompt' only if it is
available.