The overlay is not a proper overlay

One of the usescases for overlays is using nixpkgs' splicing for cross-compilation. However, as the overlay exports a static package that doesn't use final.callPackage from overlays, the splicing is lost.

nix-repl> pkgs = import <nixpkgs> { overlays = [(builtins.getFlake "github:mitchellh/zig-overlay").overlays.default]; }

nix-repl> :b pkgs.pkgsCross.aarch64-multiplatform.zigpkgs.master
error: a 'aarch64-linux' with features {} is required to build '/nix/store/p9shafw43vf4a1508z5sn0a3fsm3dj9k-zig-linux-aarch64-0.12.0-dev.3533+e5d900268.tar.xz.drv', but I am a 'x86_64-linux' with features {benchmark, big-parallel, kvm, nixos-test}

nix-repl> :b pkgs.pkgsCross.aarch64-multiplatform.stdenv.cc

This derivation produced the following outputs:
  info -> /nix/store/0wb6b7lz1xndy419ffi5vdfwl7lhj5hw-aarch64-unknown-linux-gnu-gcc-wrapper-13.2.0-info
  man -> /nix/store/f01dvcx0dd5ikwj7ycm83fm3rcgcxamg-aarch64-unknown-linux-gnu-gcc-wrapper-13.2.0-man
  out -> /nix/store/pic9zq502bybas3l0z0ymqdzkacx2h6l-aarch64-unknown-linux-gnu-gcc-wrapper-13.2.0

Note that I don't plan to use this (in fact I haven't even started my Zig journey), but just wanted to inform about this nix thing

Start at overlays.default and trace how the static Zig package is exported, comparing it with the final.callPackage path. Reproduce the pkgs.pkgsCross.aarch64-multiplatform.zigpkgs.master command and verify that the resulting derivation preserves the requested target instead of requiring aarch64-linux on an x86_64-linux host. Done means cross-compilation splicing works through the overlay.