Signed-off-by: Petr Vorel <petr.vorel@gmail.com>

It seems like a poor default for various downstream toolchains. We can't
anticipate the compiler warnings for future compiler versions and older
ones are prone to false positives. Also, older gdbus-codegen is known
to generate code that triggers compiler warnings.

Let's keep it enabled for maintainer builds and distcheck so that we're
sure a tool chain that builds releases without warnings exists.

Signed-off-by: Thomas Haller <thaller@redhat.com>

libndp has existed for a while now. 1.0 was released six months
ago. So drop the submodule and just require an installed package.

jhbuild (in the suggested configuration) passes --disable-static, but
we need static libndp at least. So tweak autogen.sh to ensure that
happens.

Previously we'd just blindly continue if e.g. autoreconf failed.

This way we do the right thing for tarball builds.

Split srcdir work and builddir work more explicitely,
and fixes a newly introduced issue (git work done out
of the srcdir section).

And change src/main.c to use the local allocation macros.  This
results in much cleaner code, as one can see from the diff.

Because libgsystem is designed for nonrecursive make, it fits best in
the current recursive setup if we build . first.  This will be a lot
nicer when we switch NM to a nonrecursive setup.