weston: add PACKAGECONFIG to build with systemd-login support
Automatically enable this support for distributions which have
systemd in DISTRO_FEATURES.
We add additional patches to weston, backported from Weston
git, to support the newer single libsystemd pkg-config file
and to make the enabling of systemd-login support explicit.
Signed-off-by: Joshua Lock <joshua.lock@collabora.co.uk> Signed-off-by: Ross Burton <ross.burton@intel.com>
