[llvm] [SDag] Fold saddo[_carry] with bitwise-not argument to ssubo[_carry] (PR #66571)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

Needing "--disable-undef-input" can usually be addressed with freeze nodes on the inputs: https://alive2.llvm.org/ce/z/tiDhDv (had to reduce type size to get alive2 to complete).

CC @nikic who might have some thoughts

https://github.com/llvm/llvm-project/pull/66571