Lower jump height on non-x86/x86_64

[zturtleman]

On non-x86/x86_64, player origin rounding causes lower jump height. (It only affects the server / offline play.)

Older Quake 3 use round to nearest instead of round toward zero. This is handled in Lilium Arena Classic on x86 and x86_64 but not other architectures. This is possible to fix in the engine.

This also affects Lilium Voyager: clover-moe/lilium-voyager#13.