build-sys: merge libsystemd-label convenience lib
Stop to pretend that we can split selinux related code from other.
We have too many cross-references and it breaks all the time and
I am no longer willing to maintain that mess for no real benefit.
We currently have cyclic dependencies which are only resolved on
machines with gc-sections toolchains. We need a simpler and at the
same time more strict model to manage our convenienc libraries and
linking.
The first thing to give up is the "optimization" of not linking
libselinux for a very few tools. If that is an issue, please fix
the mess that libselinux creates in selinux itself, and do not ask
consumers to work around it.