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Okay, I misunderstood the stack. It's clearly not using any mono stuff, so `sudo apt install libgc-dev` fixed the situation and I can move forward.
Final list deplist to install #gnupoke on #ubuntu for me was:
`sudo apt install tcl-dev libgc-dev libjson-c-dev libreadline-dev`.
Now we `make`... GNU software is so 80s, omg. :3