The atomic.cmp.swap promotion logic is wrong: it

The atomic.cmp.swap promotion logic is wrong: it
simply does the atomic.cmp.swap on the larger type,
which means it blows away whatever is sitting in
the bytes just after the memory location, i.e.
causes a buffer overflow.  This really requires
target specific code, which is why LegalizeTypes
doesn't try to handle this case generically.  The
existing (wrong) code in LegalizeDAG will go away
automatically once the type legalization code is
removed from LegalizeDAG so I'm leaving it there
for the moment.  Meanwhile, don't test for this
feature.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@53669 91177308-0d34-0410-b5e6-96231b3b80d8