Use `autoreconf` from autotools in `xdt-autogen`

We run "manually" multiple scripts in xdt-autogen : libtoolize, gtkdocize, automake, autoheader, autoconf etc

autoreconf can be used to unify all theses steps with one run, which will detect what is needed.

See:

• https://www.gnu.org/software/autoconf/manual/autoconf-2.69/autoconf.html#autoreconf-Invocation
• https://wiki.debian.org/Autoreconf