ioctl

This started as a discussion over at #124.

Users will need some way to control the settings for framebuffer/sound (resolution, etc.) For null0, I don't want them to have control of these things (fixed sound output, and window-size) so I recommend a permission-denied style error, if a config-flag is set to not allow making changes. I think some options should still be ignored, like color-depth (since this will greatly complicate the rendering.)

Some reference:

• fbset is a util that uses ioctl to get/set framebuffer settings. I think a minimal implementation should support compiling this to WASI, and running it with various options.
• linux fb where this is all defined

I think my cmem_helpers might be very helpful for managing the structs that are passed back & forth.

Start with discussion #124, fbset.c, the Linux fb.h definitions, and the referenced cmem_helpers project. Define the minimal ioctl surface needed to compile and run fbset under WASI, including permission-denied behavior for restricted framebuffer and sound settings and ignored color-depth changes.