The typing of SpeculativeSafeIntegerSubtract didn't include -0, and the
SimplifiedLowering rules for SpeculativeSafeIntegerSubtract didn't
properly handle the case of `-0 - 0`, but would always pass Word32
truncations.

Bug: chromium:913296
Change-Id: I0e5a401f075db8b349a5579e1e294df97378ea49
Reviewed-on: https://chromium-review.googlesource.com/c/1370042Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58147}