libc: define __strtok_r

Needed by memcached.

Signed-off-by: Tomasz Grabiec <tgrabiec@cloudius-systems.com>
Reviewed-by: Nadav Har'El <nyh@cloudius-systems.com>
Signed-off-by: Avi Kivity <avi@cloudius-systems.com>
runtime: add stub for sysctl()

Needed by memcached, link time.

Signed-off-by: Tomasz Grabiec <tgrabiec@cloudius-systems.com>
Reviewed-by: Nadav Har'El <nyh@cloudius-systems.com>
Signed-off-by: Avi Kivity <avi@cloudius-systems.com>