swift234

Avoid UB in RelativePointer on 32-bit platforms.

We really want to apply offsets using wrapping (unsigned) arithmetic, albeit with sign extension. This is significant on 32-bit platforms, where "far" addresses could be more than 2GB apart, but still relative-referenced using 32-bit signed values, and offset addition could end up wrapping around. Factor the logic to add an offset to a pointer out into a function that performs the sacred casting dance to appease the UB gods.