Comment # 11 on bug 1201802 from Ludwig Nussel

The situation is a bit silly. We actually only need to set
XDG_CONFIG_DIRS=/etc/xdg:/usr/local/etc/xdg:/usr/etc/xdg

The rest is legacy stuff that we should just get rid of. If someone seriously
wants to have /opt/kde3 still then the packages delivering that should also
provide the environment.

So instead of program code we could just set above static value. Unfortunately
what ever the systemd environment generators (like
systemd-environment-d-generator(8)) produce doesn't seem to be exported into
shells, eg when logging in via ssh.

We could use pam for that but the pr to support distro config files in /usr is
stuck (https://github.com/linux-pam/linux-pam/pull/408). Would only support one
file anyway, no drop-ins :-(

A simple option would be to just duplicate the setting. Ie have aaa_base
install /usr/lib/environment.d/50-xdg.conf as well as
/usr/etc/profile.d/xdg-environment.* but reduce the latter to only export
XDG_CONFIG_DIRS=/etc/xdg:/usr/local/etc/xdg:/usr/etc/xdg