Add SDL_list.{c,h} to sdl2.py

[1bsyl]

two new files:
src/SDL_list.c
src/SDL_list.h
because of this SDL2 files added (libsdl-org/SDL@1c9299b) , you'll probably need to add it to :
https://github.com/emscripten-core/emscripten/blob/main/tools/ports/sdl2.py

cc @ericoporto

[ericoporto]

@1bsyl this can be closed now.

[1bsyl]

@ericoporto thanks