Maint: gnulib: Update gnulib for build changes.

Now that we are using gnulib's own build stuff, including libtool, we
need to update various macros to reflect those changes. These changes
would also be done by running "make gnulib-update", but that would also
update all the other gnulib stuff which seems like too much for the
moment. It's easy enough to apply by hand.

This was originally written by Jan Pokorný as part of
https://github.com/ClusterLabs/pacemaker/pull/1756.