package/polkit: properly autoreconf

0001-make-netgroup-support-optional.patch patches configure.ac, but we
don't autoreconf the package, which is not good.

However, simply adding AUTORECONF = YES is not sufficient: polkit
Makefile.am use the automake conditional HAVE_INTROSPECTION, which is
"available" only when the gobject-introspection m4 file is installed.

Since we don't want to make gobject-introspection a mandatory
dependency of polkit, we take a simpler route: add a copy of
introspection.m4 into the polkit source tree. This is only a 142 lines
file, and it can be dropped when
0001-make-netgroup-support-optional.patch is merged upstream.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>