Update bundled SDL2 to 2.0.12

[aclysma]

This would resolve #1025

The patch that was removed was added upstream here: spurious/SDL-mirror@85acfec#diff-af3b638bc2a3e6c650974192a53c7291

The patch required for #1025 should be included as well: spurious/SDL-mirror@97b93a8#diff-af3b638bc2a3e6c650974192a53c7291

The patch based on this commit remains: spurious/SDL-mirror@86c309a#diff-af3b638bc2a3e6c650974192a53c7291

[aclysma]

On testing:

• I was able to run the game of life example on macOS
• Some things failed to link for me on macOS, but they failed to link for me on current latest as well.

This is not thoroughly tested, just trying to help on #1025 because I think @uhuntu has already had to bounce through multiple projects to track this down and I feel that properly working IME is very important.

[Cobrand]

It looks great, thanks! I tested it both with bundled and without and linux and nothing unusual.

[Cobrand]

sdl2-sys 0.34.3 has been pushed on crates.io. sdl2 itself is unchanged since 0.34.3, technically a cargo update in your command line should be enough to update sdl2-sys to the latest version.