XInputCheck is an XInput check abstracted away from SDL.

The content of xinputcheck.c is originally from SDL Hg c7932bb6dcee.
The files used are "src/joystick/windows/SDL_dinputjoystick.c" and
"include/SDL_stdinc.h".

If you need to update this file, please arrange the code such that
it is possible to copy/paste directly from SDL. This makes code
sharing easier! Right now, the SDL_IsXInputDevice is directly
copied from SDL.
