Package for reference:

{ stdenv, lib, fetchFromGitHub, glslang, meson, ninja, wine, pkgsCross }:

stdenv.mkDerivation rec {
  pname = "dxvk-installer";
  version = "1.9";

  src = fetchFromGitHub {
    owner = "doitsujin";
    repo = "dxvk";
    rev = "v${version}";
    sha256 = "01db23ncbrrq0cqnp25fg5plp88v5i5ri0i38m0wida8mw3mmjsa";
  };

  mesonFlags = [ "--cross-file build-win64.txt" "--buildtype release" ];
  nativeBuildInputs = [
    glslang
    meson
    ninja
    pkgsCross.mingwW64.buildPackages.gcc
    pkgsCross.mingwW64.windows.mingw_w64
    pkgsCross.mingwW64.windows.mingw_w64_headers
    wine
  ];
}

Package for reference:

{ stdenv, lib, fetchFromGitHub, glslang, meson, ninja, wine, pkgsCross }:

stdenv.mkDerivation rec {
  pname = "dxvk-installer";
  version = "1.9";

  src = fetchFromGitHub {
    owner = "doitsujin";
    repo = "dxvk";
    rev = "v${version}";
    sha256 = "01db23ncbrrq0cqnp25fg5plp88v5i5ri0i38m0wida8mw3mmjsa";
  };

  mesonFlags = [ "--cross-file build-win64.txt" "--buildtype release" ];
  nativeBuildInputs = [
    glslang
    meson
    ninja
    pkgsCross.mingwW64.buildPackages.gcc
    pkgsCross.mingwW64.windows.mingw_w64_headers
    wine
  ];
}

I ended up with

{ stdenv, lib, fetchFromGitHub, glslang, meson, ninja,  pkgsCross, gcc, buildPackages }:

stdenv.mkDerivation rec {
  pname = "dxvk-installer";
  version = "1.9";

  src = fetchFromGitHub {
    owner = "doitsujin";
    repo = "dxvk";
    rev = "v${version}";
    sha256 = "01db23ncbrrq0cqnp25fg5plp88v5i5ri0i38m0wida8mw3mmjsa";
  };

  mesonFlags = [ "--cross-file build-win64.txt" "--buildtype release" ];
  depsBuildBuild = [ buildPackages.stdenv.cc buildPackages.meson buildPackages.ninja ];
  depsBuildTarget = [
    pkgsCross.mingwW64.windows.mingw_w64_headers
    glslang
    buildPackages.gcc
  ];
}

called via nix-build -E 'with import <nixpkgs> {}; pkgsCross.mingwW64.callPackage ./dxvk.nix { }' but I still end up with the same error. Do I have to get mingwW64 from somewhere else now? I can't find it.

At the risk of sounding like a broken record - I still can't manage to override patchelf for my cross setup only (ie. so it just affects cross packages being built).

My 'solution' was to prepend my modified patchelf to extraNativeBuildInputs in the cross stdenv. That works (it appears to end up in front of the PATH), unless a package specifies patchelf as a nativeBuildInput (for example: systemd).

All my other attempts either do nothing (e.g. overlaying pkgs.buildPackages) or affect all packages, so an evaluation ends up rebuilding large parts of my host OS.