This avoids -Werror build issues in strace, which bundles UAPI
headers, but does not include them as system headers.
Fixes commit c444cc1d8335243c5c4e636d6a26c472df85522c
("Linux: Add missing scheduler constants to <sched.h>").
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
4f5f8343c3