testing/libretro-atari800: upgrade to 0_git20240924
https://github.com/libretro/libretro-atari800/compare/beab30e...39380a6
Also resolves a rebuild error with gcc 14.
https://github.com/libretro/libretro-atari800/compare/beab30e...39380a6
Also resolves a rebuild error with gcc 14.