linux-user: Handle SOCK_CLOEXEC/NONBLOCK if unavailable on host

If the host lacks SOCK_CLOEXEC, bail out with -EINVAL.
If the host lacks SOCK_ONONBLOCK, try to emulate it with fcntl()
and O_NONBLOCK.

Signed-off-by: Edgar E. Iglesias <edgar.iglesias@gmail.com>
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>