add minimal ModemManager for use with GPS

can't use the regular nixos modem-manager because it doesn't
cross-compile

configuration.nix

@@ -12,6 +12,8 @@ let
     makeFlags = ["prefix=${placeholder "out"}"];
   };
 
+  modemmanager_ = pkgs.callPackage ./modem-manager.nix {};
+
   drm-framebuffer =  pkgs.stdenv.mkDerivation {
     name = "drm-framebuffer";
     src = pkgs.fetchFromGitHub {

modem-manager.nix

@@ -0,0 +1,88 @@
+{
+  stdenv,
+  fetchFromGitLab,
+  libxslt,
+  bash, # shebangs in share/ModemManager/fcc-unlock.available.d/,
+  bash-completion,
+  dbus,
+  gettext,
+  glib,
+  libgudev,
+  libqmi,
+  meson,
+  ninja,
+  cmake,
+  pkg-config,
+  python3,
+  systemd,
+  pkgsBuildBuild,
+  buildPackages
+}: stdenv.mkDerivation rec {
+  pname = "modemmanager";
+  version = "1.22.0";
+
+  src = fetchFromGitLab {
+    domain = "gitlab.freedesktop.org";
+    owner = "mobile-broadband";
+    repo = "ModemManager";
+    rev = version;
+    hash = "sha256-/D9b2rCCUhpDCUfSNAWR65+3EyUywzFdH1R17eSKRDo=";
+  };
+  patches = [
+    /home/dan/src/nixpkgs/pkgs/tools/networking/modemmanager/no-dummy-dirs-in-sysconfdir.patch
+  ];
+  nativeBuildInputs = [
+    meson
+    ninja
+    # gobject-introspection
+    gettext
+    pkg-config
+    libxslt
+    python3
+    cmake
+    glib # for gdbus-codegen
+  ];
+
+  buildInputs = [
+    glib
+    libgudev
+    # polkit
+     pkg-config
+    # ppp
+    # libmbim
+    libqmi
+    systemd
+    bash-completion
+    dbus
+#    cmake
+    bash # shebangs in share/ModemManager/fcc-unlock.available.d/
+  ];
+
+  mesonFlags = [
+    "-Dudevdir=${placeholder "out"}/lib/udev"
+    "-Ddbus_policy_dir=${placeholder "out"}/share/dbus-1/system.d"
+    "--sysconfdir=/etc"
+    "--localstatedir=/var"
+    "-Dvapi=false"
+    "-Dmbim=false"
+    "-Dqmi=true"
+    "-Dqrtr=false"
+    "-Dpolkit=no"
+    "-Dplugin_foxconn=disabled"
+    "-Dman=false"
+    "-Dexamples=false"
+    "-Dtests=false"
+    "-Dintrospection=false"
+  ];
+
+  postPatch = ''
+    env | grep PKG
+    mkdir bin
+    PATH=${buildPackages.pkg-config}/bin:$PATH
+    PATH=$PWD/bin:$PATH
+    ln -s ${buildPackages.pkg-config}/bin/$PKG_CONFIG bin/pkg-config
+    echo $PATH | sed 's/:/\n/g' | grep pkg
+    type pkg-config
+    patchShebangs tools/test-modemmanager-service.py
+  '';
+}