[PATCH] x86-64: Lose constraints on cmpxchg

While only cosmetic for x86-64, this adjusts the cmpxchg code appearantly
inherited from i386 to use more generic constraints.

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>