Log Message:
emulators: add libretro-gearboy

Libretro is a simple but powerful development interface that allows for the
easy creation of emulators, games and multimedia applications that can plug
straight into any libretro-compatible frontend. This development interface is
open to others so that they can run these pluggable emulator and game cores
also in their own programs or devices.

Gearboy is a cross-platform Game Boy / GameBoy Color emulator written in C++.