debian/rules: use autogen.sh so we can build directly from git

Refs T770. Similar to D1435.

Reviewed-by: Philip Withnall <philip.withnall@collabora.co.uk>
Signed-off-by: Simon McVittie <simon.mcvittie@collabora.co.uk>
Differential Revision: https://phabricator.apertis.org/D1641

debian/rules

@@ -4,6 +4,9 @@
 %:
 	dh $@ --with autoreconf --with systemd
 
+override_dh_autoreconf:
+	NOCONFIGURE=1 dh_autoreconf ./autogen.sh --
+
 override_dh_auto_configure:
 	dh_auto_configure -- --enable-gtk-doc=yes