[SystemZ] Custom-expand ATOMIC_CMP_AND_SWAP_WITH_SUCCESS

[SystemZ] Custom-expand ATOMIC_CMP_AND_SWAP_WITH_SUCCESS

The SystemZ compare-and-swap instructions already provide the "success"
indication via a condition-code value, so the default expansion of those
operations generates an unnecessary extra comparsion.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@314428 91177308-0d34-0410-b5e6-96231b3b80d8