The version of AtomicSDNode::AtomicSDNode used (only) for

cmp-and-swap reversed the Cmp and Swap arguments; comments
make it clear this is unintentional.  Unfortunately, the
x86 BE had a compensating reversal, which is removed here.
PPC is OK.

From inspection of the Alpha code I think it is OK, but
if somebody has that platform please check it out.  I
cannot test on that platform.

llvm-svn: 56091