Init systems and build systems are the same thing

Think about it a second.
That's right, with a couple of shell functions you could have a script that both starts up your OS and compiles your code. Just define your ultimate targets (start agetty, compile main.c), dependencies (mount drives, compile foo.c) how to resolve each target, and how to check whether each target is already resolved.
Higher-level programs can serve as a front-end and check circular dependencies ahead of time.

It's got to be a few dozen lines maximum. systemd and make can fuck off.

How many times can we write topological sort of a directed graph and call it original software?