A move towards using the generic ISD::ABDU nodes on more backends
Also support ISD::ABDS for v4i32 types using the existing signbit flip trick
PowerPC has a select(icmp_ugt(x,y),sub(x,y),sub(y,x)) -> abdu(x,y) that I intend to move to DAGCombiner in a future patch.
I don't think the PPCISD::VABSD(X,Y,1) v4i32 combine was legal (at least alive2 didn't think so) - so I've removed it.