This becomes more of an issue when implementing the Intl mathematical
value, where negative zero is treated as a special enum value. In that
case, we already previously changed the value from -0 to +0 in step 1b.
Entering the branch for step 4 will then set it back to -0.
The math that follows after these steps worked fine with both +0/-0, but
assertions will be reached in the Intl MV implementation.
20533c2594