ar x /nix/store/y7z59i6l25m46jdqgqxjpbzsq4npd9mb-compat-netbsd-9.1-powerpc-unknown-linux-musl/lib/libnbcompat.a db.lo
# file db.lo
db.lo: ELF 64-bit LSB relocatable, x86-64, version 1 (SYSV), not stripped

Git history tells me it should cross compile, but I don't see how that's supposed to work looking at the source: https://github.com/NixOS/nixpkgs/blob/master/pkgs/os-specific/bsd/netbsd/default.nix#L160

    # the build system re-runs `./configure` with `HOST_CC` (which is their
    # name for Build CC) as a compiler to make `defs.mk`, which is installed
    depsBuildBuild = [ buildPackages.stdenv.cc ] ++ commonDeps;
    HOST_CC = "${buildPackages.stdenv.cc.targetPrefix}cc";

In reply to @rick:matrix.ciphernetics.nl
Hey! Just found out there's a room for cross-compilation :)

since you don't have access to nixpkgsFun it is a bit more cumbersome to emulate, something like this should work:

self: super: {
  pkgsCross = super.pkgsCross // {
    mySystem = import super.path (super.config // {
      crossSystem = mySystemDefinition;
    });
  };
}