nixpkgs has a notion of "native cross compiling". My understanding is that this amounts to having prefixes on our executables but not actually cross compiling as far as Hadrian is concerned. The use case is something like a fully statically linked package set, or one where we are using a different libc. Currently haskell.nix and perhaps soon nixpkgs (See this https://github.com/NixOS/nixpkgs/pull/383165) work around this by editing the configure script. I'm proposing we add a flag to the configure script that let's you specify that we aren't doing cross compiling even if `$target != $host`.