This patch fixes the condition code for 'compare' llvm IR in the expansion of *absdiff* intrinsic.
LangRef doc is updated to reflect this change.
Test case is divided into two, based on the data width(128/256 bit). Also updated the tests to make it non-fragile.
I'd phrase this differently, and say that the intermediate calculations are computed using infinitely-precise unsigned arithmetic. That's similar to the language we used for inbounds GEPs.