For what it's worth, that same github user already reverse-engineered the game : https://github.com/skynettx/raptor and this one should be able to compile on modern platforms.
There is probably a story behind the source release, I wonder what it is...
Took some time to test. It builds pretty easily (on Ubuntu, at least), the asset extraction is bit more involved (hint : you WANT to read and understand tools/extract.sh) but overall quite doable.
It runs, renders, basic camera controls work. But I haven't managed to take off. Still rather impressive and full of promises.