New port: games/retroarch

RetroArch is the reference frontend for the libretro API. Popular examples
of implementations for this API includes videogame system emulators and
game engines, but also more generalized 3D programs. These programs are
instantiated as dynamic libraries. We refer to these as "libretro cores".

WWW: http://github.com/libretro/RetroArch

PR: 204347
Submitted by: yuri@rawbw.com