add sched_getaffinity stub and implement sysconf(_SC_OPEN_MAX)

they are needed to start Erlang Shell

Signed-off-by: bhuztez <bhuztez@gmail.com>
Reviewed-by: Nadav Har'El <nyh@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>