x86*: Return syscall error for lll_futex_wake.

It is very very possible that the futex syscall returns an
error and that the caller of lll_futex_wake may want to
look at that error and propagate the failure.

This patch allows a caller to see the syscall error.

There are no users of the syscall error at present, but
future cleanups are now be able to check for the error.

--

nplt/

2013-06-10  Carlos O'Donell  <carlos@redhat.com>

	* sysdeps/unix/sysv/linux/i386/lowlevellock.h
	(lll_futex_wake): Return syscall error.
	* sysdeps/unix/sysv/linux/x86_64/lowlevellock.h
	(lll_futex_wake): Return syscall error.