sys/posix: use __restrict instead of restrict
sys/posix: use __restrict instead of restrict

RIOT-OS/RIOT,kaspar030/RIOT,kYc0o/RIOT,jasonatran/RIOT,RIOT-OS/RIOT,miri64/RIOT,jasonatran/RIOT,RIOT-OS/RIOT,ant9000/RIOT,ant9000/RIOT,ant9000/RIOT,jasonatran/RIOT,kYc0o/RIOT,kaspar030/RIOT,RIOT-OS/RIOT,kYc0o/RIOT,miri64/RIOT,miri64/RIOT,miri64/RIOT,jasonatran/RIOT,jasonatran/RIOT,kaspar030/RIOT,miri64/RIOT,kaspar030/RIOT,RIOT-OS/RIOT,kYc0o/RIOT,ant9000/RIOT,ant9000/RIOT,kYc0o/RIOT,kaspar030/RIOT