[llvm] [DAGCombiner] Add pattern matching for negated subtraction in ABDU selection (PR #156217)

[Simon Pilgrim via llvm-commits]

https://github.com/RKSimon commented:

How come we're not already catching this with `neg(sub(x,y)) -> sub(y,x)`?

https://github.com/llvm/llvm-project/pull/156217