For SELinux, refpolicy has its own container policy which is different
from what upstream uses at https://github.com/containers/container-selinux.
SELINUXOPT controls this and seemingly nothing else. selinux-go doesn't
seem to use libselinux either. So, just keep USE=selinux for the policy
dep (which is an exemption to the "no runtime USE flags" rule that we do
in various places).
Closes: https://bugs.gentoo.org/980033
Signed-off-by: Sam James <sam@gentoo.org>