I would argue that a complete replacement for what a GNU person would call "binutils" is a ship of theseus situation. Or, replacement of core dependency on GCC by llvm.
It's still BSD. It's still under the derivatives of the 2, 3, ISC and MIT clause licence.
So you could recurse. For a tool like LLVM which is bound by some licence, if you e.g. replaced it by rust, would it still be bound? It's a good question. I think (personally) that the licence acceptance is to the goods not the language, it's an assert by the controlling authority and isn't bound to C or ASM. If they wrote the rust, and distributed the rust to deliver the function, the function is what makes it "ship of theseus" or "my grandfathers axe"
(I am not a lawyer)
Copyright has to be quite specifically linked to your work otherwise it's much more like a patent: you can't build X because I did. With copyright you can't build X but you can build Y and Z and they can replicate everything X does (that isn't encumbered with patents). In the case of games we have seen famous examples like Zynga being relentlessly-copied by Vostu, or Rocket Internet investing in "X but for Europe" where they clone entire companies. So there's some good examples of how copyright itself isn't even necessarily a defensible product when the output is quite close (almost identical with Vostu). It's hard to believe open source is actually more defensible!
https://techcrunch.com/2011/06/16/war-zynga-sues-the-hell-ou...
