Motivation for this change

Looks like teeworlds offers cmake support
and since it is mentioned first in their README
I gave it a go and ... 😁 🎉

This fixes long-standing issues I've had building teeworlds
with more exotic compilers
(including clang? but havne't tried it using nixpkgs-master lately...)
and makes it possible to greatly simplify the expression
with all the same files installed AFAICT.

I noticed bam now has no consumers in-tree,
but I'm content letting it sit there (and maybe bitrot if untested)
as long as it doesn't make things too awkward when we're hanging
and it sees teeworlds expression happier and healthier than ever before
and while that truly brings joy it hurts and is a constant reminder of
its mistakes and weaknesses and what could have been ....
well so I think we can maybe hold off on evicting it for now.
That seems kinda cruel. Likely teeworlds wouldn't be what it is today
if not for all bam has done for it.

Okay anyway >> <<.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

I've only tested the client?
And now that there's a build system we're familiar with... if anyone's
curious we might have some options to poke at.

(sorry bam ;3)