[llvm] [SeparateConstOffsetFromGEP] Decompose constant xor operand if possible (PR #135788)

[Juan Manuel Martinez Caamaño via llvm-commits]

https://github.com/jmmartinez approved this pull request.

LGTM, but check my last comment to confirm we either handle unreachable basic-blocks / or that they are impossible.

https://github.com/llvm/llvm-project/pull/135788