Fix x86's XALUO lowering to return its replacement values instead

Fix x86's XALUO lowering to return its replacement values instead
of doing the RAUW calls for the overflow value itself. This makes
it more consistent with how the rest of LegalizeDAG works.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@135788 91177308-0d34-0410-b5e6-96231b3b80d8