gst/gst.c: use _exit() instead of exit() in our forked child; this ensures that none...

gst/gst.c: use _exit() instead of exit() in our forked child; this ensures that none of the registered exit handlers ...

Original commit message from CVS:
* gst/gst.c: (init_post):
use _exit() instead of exit() in our forked child; this ensures
that none of the registered exit handlers from whatever is using
GStreamer get executed.  This fixes gnome-mixer-applet failing
to load, because ORBit would shut down.
Spotted by: Edward Hervey  <edward@fluendo.com>
Fix suggested by: Tim-Philipp Müller  <tim at centricular dot net>
Fixes #344474