Some of the DCHECK_LT assertions in GenerateBranches were generating
signed-vs-unsigned comparisons in SM. While I was looking at this code,
it seemed reasonable to just fix the whole thing to use uc32/uint32_t
where appropriate.

Bug: v8:11380
Change-Id: I7e27fb7e34ce962349d7204d6306217292746e33
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2666986Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72557}