nixos-config/nixos/system/all/packages/llvm-config-dummy.nix

{ pkgs, config, lib, ... }:
with pkgs.lib; {
  environment.systemPackages =
    let
      llvm = pkgs.llvm;
      llvm-config = pkgs.writers.writeBashBin "llvm-config" ''
        while [[ $# -gt 0 ]]; do
          arg="$1"
          case $arg in
            --assertion-mode)
              echo "OFF"
              ;;
            --bindir)
              echo "${getBin llvm}/bin"
              ;;
            --libdir)
              echo "${getLib llvm}/lib"
              ;;
            --includedir)
              echo "${getDev llvm}/include"
              ;;
            --prefix)
              echo "${llvm.out}"
              ;;
            --src-root)
              echo "/build/llvm";
              ;;
            --obj-root)
              echo "/build/llvm/build";
              ;;
            --cmakedir)
              echo "${getDev llvm}/lib/cmake/llvm"
              ;;
            *)
              echo "Unhandled argument '$arg' passed to dummy llvm-config!"
              exit 1
          esac
          shift
        done
      '';
    in
    [ llvm-config ];
}