Automatically init submodules if there are no sources in sdl2-sys/SDL.
Automatically init submodules if there are no sources in sdl2-sys/SDL.

Cobrand/rust-sdl2,Cobrand/rust-sdl2,Cobrand/rust-sdl2,Rust-SDL2/rust-sdl2,Rust-SDL2/rust-sdl2,Rust-SDL2/rust-sdl2