Idea: target specific sdl_bindings.rs

[antonilol]

We currently have 1 sdl_bindings.rs file that is used on every platform, but these bindings are generated on linux, so contain linux specific things.
Should we split this in 3 files maybe? (linux, mac and windows)
Or more? (1 per target we have pregenerated bindings for, other targets need users to run bindgen)

[antonilol]

The windows builds have recently been failing because the layout of some X11 structs is incorrect. I am pretty sure we should not have X11 structs in the bindings used on windows