Well in this case, the program hardly needs an operating system at all. The only library calls required by default are printf and fgets. Assuming there's a way to get text and print it, it can run. There also needs to be about 50-100k of RAM when the interpreter is loaded into memory.
well, language features tend to need OS/system features.
for example, trying to support dynamically loaded libraries, or leveraging multiple cores. It might not be relevant for a little toy language, but when you go to the next level, you will hit this and by then, it might be too late and you're stuck with a sub awesome choice.
Once you need to do those things, C is where you'll find the most pre-existing tooling pretty much regardless what platform you're on.
(note that personally I strongly believe in self-hosting compilers, but not because it's the easy approach, but because it's not: it forces you to make sure you can support all of the hard bits yourself; if I wanted easy, I'd pick C)
You need the ability to make system calls, and you probably want the ability to call the standard library, which means supporting the "C" ABI (kind of a misnomer - system libraries might be written in e.g. Pascal and you wouldn't notice the difference, they just have to support the same calling convention. But you do need to be interoperable with C)
