The only way to get a minus zero result from subtraction is
(-0) - (+0) = -0, hence checking for minus zero on the RHS is
redundant. This is causing some unnecessary deoptimisations
in Box2D from Octane on 32-bit platforms.

BUG=

Review-Url: https://codereview.chromium.org/2410883003
Cr-Commit-Position: refs/heads/master@{#40207}