package/musl: Make scheduler functions Linux-compatible

package/musl: Make scheduler functions Linux-compatible

The POSIX functions sched_getscheduler(), sched_setscheduler(),
sched_getparam(), sched_setparam() are technically not correctly
implemented by the Linux syscalls of the same name, because what the
kernel calls a PID and what POSIX calls a PID isn't truly the same,
resulting in somewhat different semantics as to what these functions
exactly apply to.
Details: https://sourceware.org/bugzilla/show_bug.cgi?id=14829

Since the musl developers put a high premium on POSIX compliance, they
deliberately implement these functions to return -ENOSYS instead of
relaying them to the respective Linux syscalls as glibc/uClibc do.

Unfortunally this breaks virtually all Linux programs using these
functions under musl. For example running 'chrt -p 1' fails with
'Function not implemented' on a musl-libc based system.
In particular, it affects embedded systems using these interfaces
for scheduling real-time processes.

As it seems unfeasible to fix all affected programs to manually use
syscall wrappers instead of the libc functions, make musl behave the
Linux way.

Signed-off-by: Stefan Nickl <Stefan.Nickl@gmail.com>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>