gettext-full: bootstrap to local gnulib source

gettext-full: bootstrap to local gnulib source

Using the local gnulib source during autogen.sh
allows for fine-grained control over the macros
and source files for use with gettext
but part of gnulib instead of gettext,
without having to wait for a release
or deal with gnulib as a git submodule.

This is an alternative to running autoreconf.

It also removes the need to patch macros
in the case where there is a conflict
between the source and our aclocal directory.

Signed-off-by: Michael Pratt <mcpratt@pm.me>