--- stderr
  thread 'main' panicked at /build/cosmic-settings-1.0.0-alpha.4-unstable-2024-12-17-vendor/bindgen-0.69.5/lib.rs:622:31:
  Unable to find libclang: "the `libclang` shared library at /nix/store/pcs60p9pghggp5ycs47kk53cddvgym86-clang-riscv64-unknown-linux-gnu-18.1.8-lib/lib/libclang.so.18.1.8 could not be opened: /nix/store/pcs60p9pghggp5ycs47kk53cddvgym86-clang-riscv64-unknown-linux-gnu-18.1.8-lib/lib/libclang.so.18.1.8: cannot open shared object file: No such file or directory"
  note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
warning: build failed, waiting for other jobs to finish..

Rip

let
  someRevOnMaster = "742e83951eefc0a0a74dd95a6523300dacfb4238";
  inherit
    (import (builtins.getFlake "github:nixos/nixpkgs/${someRevOnMaster}") {
      system = "aarch64-linux";
    })
    pkgsCross
    ;
in
builtins.head (
  builtins.filter (drv: drv.name == "X11-fonts")
    (pkgsCross.riscv64.nixos {
      fonts.fontDir.enable = true;
      boot.isContainer = true;
    }).config.environment.systemPackages
)

This builds

let
  nixpkgs = builtins.getFlake "github:nixos/nixpkgs/d29ab98cd4a70a387b8ceea3e930b3340d41ac5a";
in
builtins.head (
  builtins.filter (drv: drv.name == "X11-fonts")
    (import "${nixpkgs}/nixos/lib/eval-config.nix" {
      modules = [
        {
          fonts.fontDir.enable = true;
          boot.isContainer = true;
          nixpkgs.crossSystem = { system = "riscv64-linux"; };
          nixpkgs.localSystem = { system = "aarch64-linux"; };
        }
      ];
    }).config.environment.systemPackages
)

This throws an exec format error

$ nix eval --file test.nix drvPath
"/nix/store/0gp81b50wg2bf2dbqswkbhvy21i8x552-X11-fonts.drv"
$ nix eval --file test-fail.nix drvPath
"/nix/store/0gp81b50wg2bf2dbqswkbhvy21i8x552-X11-fonts.drv"

$ nix build --file test.nix --rebuild
evaluation warning: system.stateVersion is not set, defaulting to 25.05. Read why this matters on https://nixos.org/manual/nixos/stable/options.html#opt-system.stateVersion.
error: a 'aarch64-linux' with features {} is required to build '/nix/store/0gp81b50wg2bf2dbqswkbhvy21i8x552-X11-fonts.drv', but I am a 'x86_64-linux' with features {benchmark, big-parallel, ca-derivations, kvm, nixos-test}

I got the drv from cache it seems

1. /nix/store/0gp81b50wg2bf2dbqswkbhvy21i8x552-X11-fonts.drv
2. /nix/store/1xfdmcvvjc1s57lp4yfq5x5cl9zva9bk-X11-fonts.drv