gspawn: Use fcntl() to work around systems which don’t support O_CLOEXEC
gspawn: Use fcntl() to work around systems which don’t support O_CLOEXEC

Somehow, we are still limping along with partial support for OS X
<10.7.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

https://gitlab.gnome.org/GNOME/glib/issues/1488

endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib