Also, VGMStream should compile on a POSIX-like system, MacOS X included (the console line player, not the Winamp plugin, obviously). hcs says the program assumes little-endian for now, so I can't say it will work on PPC based systems though.
I checked if it would build out of the box, but it depends on Audacious, an apparently Linux-only(?) music player which uses GTK. Can't tell for sure yet because the Audacious website is down and apparently has been for a couple of months.