Align stack to 16 bytes when calling __gettimeofday

Subtract stack by 24 bytes instead of 16 bytes so that stack is aligned
to 16 bytes when calling __gettimeofday.

	[BZ #18661]
	* sysdeps/unix/sysv/linux/x86_64/lowlevellock.S
	(__lll_timedwait_tid): Align stack to 16 bytes when calling
	__gettimeofday.