[llvm] add scmp and ucmp to SelectionDAG.cpp (PR #84681)

[Miguel Raz Guzmán Macedo via llvm-commits]

miguelraz wrote:

Closing due to too many git headaches and restarting on fresh main with https://github.com/llvm/llvm-project/pull/85822

https://github.com/llvm/llvm-project/pull/84681