[llvm] [X86] Transform `(xor x, SIGN_BIT)` -> `(add x, SIGN_BIT)` 32 bit and smaller scalars (PR #83659)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

We already do some of this in X86DAGToDAGISel::matchAddressRecursively - maybe see why these cases weren't working there?

https://github.com/llvm/llvm-project/pull/83659