Avoid PLT when calling __sched_getaffinity_new

This patch adds an internal entry for __sched_getaffinity_new so that
__sched_getaffinity_old calls __sched_getaffinity_new without going
through PLT.

	[BZ #18822]
	* sysdeps/unix/sysv/linux/sched_getaffinity.c
	(__sched_getaffinity_new): Add libc_hidden_proto and
	libc_hidden_def.