Changes

glibc-sched.h: fix cygwin sched.h compatibility

Cygwin defines _SCHED_H_ instead of _SCHED_H, causing our header to scream.

Not sure why we didn't catch this earlier, maybe things changed in Cygwin.

Signed-off-by: Brice Goglin <Brice.Goglin@inria.fr>
(cherry picked from commit 4cf9d5126d0b636e5c0be3c44e7e4584109b05b6)