[llvm] add ucmp and scmp support to SelectionDAG (PR #85822)

[Miguel Raz Guzmán Macedo via llvm-commits]

miguelraz wrote:

@nikic I pushed this as far as I could today to try and solve the `add code to print the node to 'getOperationName'` and fold the constants in. 

It's probably atrocious code but I hit a wall of 
* not knowing how to return a constant `SDNode` of value `1` or `0`
* not knowing how to check if `N1` was signed or not

And I still am struggling with the `SVNode` APIs.

https://github.com/llvm/llvm-project/pull/85822