oslib-posix.c: Move workaround for OSX daemon() deprecation to osdep.h
The right place for "work around issues with system headers" code
is osdep.h. Move the workaround for OSX's stdlib.h emitting a
deprecation warning for daemon() to that header.
This also fixes a problem where running clean-includes on
oslib-posix.c would erroneously remove the #include <stdlib.h>
from it, breaking the workaround.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Eric Blake <eblake@redhat.com>