Here's my stupid little libretro frontend. Its input layout is hardcoded, it doesn't fully implement the libretro specification, it's unfinished, and it's not intended for general use. Don't use this. As for a licence - hell if I know. I guess it's public-domain or MIT-0, choose whichever you like.
Clownacy/clownlibretro
My really bad libretro frontend. I'm just programming this for fun: don't expect quality.
C