[llvm] [SelectionDAG] Fix condition used for unsigned subtraction overflow (PR #170896)

[Jay Foad via llvm-commits]

jayfoad wrote:

The reason is that carryout-selection.ll is a bit weird - it says the checks are autogenerated, but actually the GCN-ISEL checks are still manual. This comes from https://reviews.llvm.org/D143987, @vikramRH FYI.

Probably the easiest way to proceed is: delete the GCN-ISEL RUN line, then use the script to update all the other checks, then add back the GCN-ISEL RUN line.

https://github.com/llvm/llvm-project/pull/170896