Hide internal __sched_setparam function to allow direct access within
libc.so and libc.a without using GOT nor PLT.
__GI___sched_setparam is defined when sysdeps/unix/syscalls.list is
used to generate sched_setparam. Otherwise libc_hidden_def is needed
explicitly.
[BZ #18822]
* include/sched.h (__sched_setparam): Add libc_hidden_proto.
* posix/sched_setp.c (__sched_setparam): Add libc_hidden_def.