Revert "x86: Side-step lguest problem by only building cmpxchg8b_emu for pre-Pentium"

Revert "x86: Side-step lguest problem by only building cmpxchg8b_emu for pre-Pentium"

commit db677ffa5f5a4f15b9dad4d132b3477b80766d82 upstream.

This reverts commit ae1b22f6e46c03cede7cea234d0bf2253b4261cf.

As Linus said in 982d007a6ee: "There was something really messy about
cmpxchg8b and clone CPU's, so if you enable it on other CPUs later, do it
carefully."

This breaks lguest for those configs, but we can fix that by emulating
if we have to.

Fixes: http://bugzilla.kernel.org/show_bug.cgi?id=14884
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>