The upstream project already builds and releases for aarch64. This makes
the couple small tweaks that I found necessary for k3s to cross-compile
for aarch64.
I also ran it through nixpkgs-fmt.
This packages k3s as a single self-contained binary (as upstream k3s
does), but without having to download any impure already-built binaries.
The upstream packaging scripts are used. Due to k3s's rather complicated
packaging arrangement, this ends up being a rather long derivation.
