libc: add pthread_attr_setinheritsched to run WEBrick its ruby HTTP server

Reviewed-by: Nadav Har'El <nyh@cloudius-systems.com>
Signed-off-by: KANATSU Minoru <icc.pot.tyew272@gmail.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
random: Add a note to avoid misconception about virtio_rng_read

Signed-off-by: Raphael S. Carvalho <raphaelsc@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>