sdl2: disable DirectInput because of missing wbemcli.h

MXE/MinGW does not carry wbemcli.h, so SDL_dxjoystick will not build. This just enables the same workaround in configure as is done for Cygwin, which is to disable DirectInput and enable SDL_mmjoystick instead. That's enough to make SDL2 compile and link.

This is a known upstream issue, see https://bugzilla.libsdl.org/show_bug.cgi?id=1739. I've sent this patch there as well.

Also enabled SDL2_image, since that now builds successfully.