Was a lot easier than I expected. The software renderer is such a
godsend for quick-and-dirty ports.
Oddly enough, even on an old3DS, this actually almost runs at full
speed (hits around 40FPS in Mimiga Village).
There's a lot of work left to do before this is actually useable:
* There's no audio
* You can't save
* A proper hardware-accelerated renderer is needed