libmtp: improve cross-compilation support

It still doesn't build, but it gets further now.
Also added configurePlatforms explicitly, not strictly needed for cross,
but might help catch issues with cross earlier in some cases.

pkgs/development/libraries/libmtp/default.nix

@@ -35,10 +35,12 @@ stdenv.mkDerivation rec {
 
   propagatedBuildInputs = [ libusb1 ];
 
-  preConfigure = "./autogen.sh";
+  preConfigure = "NOCONFIGURE=1 ./autogen.sh";
 
   configureFlags = [ "--with-udev=${placeholder "out"}/lib/udev" ];
 
+  configurePlatforms = [ "build" "host" ];
+
   enableParallelBuilding = true;
 
   meta = with lib; {