Fix daemon build for no-MMU no-threads.
CLONE_VM (used in no-MMU daemon) is defined in <bits/sched.h>. A
build with threads ends up including <sched.h> via <pthread.h> via
<bits/uClibc_mutex.h>; this indirect include does not happen for a
build without threads, so this patch adds a direct <sched.h> include.
Signed-off-by: Joseph Myers <joseph@codesourcery.com>