unbound: fix cross-compilation (#370087)
Due to a check in make-derivation.nix (https://github.com/nixos/nixpkgs/blob/e4f449ab51a283676d3b520c3dbaa3eafa5025b4/pkgs/stdenv/generic/make-derivation.nix#L288),
`nativeCheckInputs` is not used. This causes cross-compilation for
unbound to fail due to the programs in `bison` not being available.
authored by Jared Baur and committed by GitHub a8f36e39 92de48d8