Add mgba recipe
This MR adds a recipe for mGBA, a Game Boy Advance emulator. Mostly works with a couple of issues.
- Extreme stutter on input.
- Saving savegames might not work yet. Only loading them.
mmaps seems to be borked on Redox. I added temporary workarounds for this.
- There's an issue with the SDL audio callbacks, caused by incorrect stack mapping. Temporary workarounds for now until it's fixed.
- The SDL/pte shutdown code started crashing recently. This affects every SDL app, not just mGBA.
- Sometimes crashes the kernel with "Grant should not exist" messages.
- Video corruption after multiple launches