Man, I can't even tell what this is supposed to be. My confusion is entirely founded. My thought process with articles like this goes something like "C in four functions, huh? Sounds like it could be clever. I'll just click and read the explanation... Oh, there isn't an explanation. Well, maybe this file will explain things! ...Nope, it's 500 lines of mostly-uncommented if-else statements. Maybe it's a compiler? I dunno!"
I'm sure there's a subset of the programming community for whom this is crystal clear on first sight, and that's great; but there's a lot more of us who could probably get the joke with a few hints, so it would be nice if you'd help out instead of declaring that if you understand it, it must be easy.
With code like this, the readability obviously isn't a high priority consideration and sometimes the exact opposite of the goal, with the impenetrability sometimes being part of its charm. This is Hacker News after all, and if your reaction to of a piece of code that describes itself as "an exercise in minimalism" is to leave a snarky comment about the lack of documentation, you should probably check your news elsewhere.
If you have any interest in the subject, the initial comment "just enough features to allow self-compilation and a bit more" should give the purpose of the code away. If not, it ought to have been a clear sign of dragons.