nixos-config/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 ];
}