testing/cemu: new aport

Currently, it builds and runs fine using clang15 (https://github.com/cemu-project/Cemu/issues/781).
I've marked it as a draft because cmake isn't finding cubeb, so I'll have to try and fix that tomorrow (I've yet to master the art of cmake).
Cubeb was missing pulseaudio-dev.
Wayland also works, but only if scaling is set to 1.0, so I've left the GDK_BACKEND=x11.
Here's some Wind Waker.