This provides backwards-compatible autolaunching behaviour, as long
as dbus-launch inherits the XDG_RUNTIME_DIR (which it presumably did
if it's going to work at all, since it must also have inherited the
DISPLAY). In particular, we go through the motions of starting the
dbus-daemon, so that we can start the "babysitter" process that will
maintain the X11 window to store the bus address.
Bug: https://bugs.freedesktop.org/show_bug.cgi?id=61301
Reviewed-by: Philip Withnall <philip.withnall@collabora.co.uk>
[smcv: decorate _dbus_lookup_user_bus with DBUS_PRIVATE_EXPORT so we
can still call it after fixing fd.o#83115; update cmake to match Autotools]
This is installed by default, but easy to filter out for embedded systems
or whatever.
Based on earlier work by Simon McVittie and Will Thompson
Bug: https://bugs.freedesktop.org/show_bug.cgi?id=34140
Reviewed-by: Simon McVittie <simon.mcvittie@collabora.co.uk>