libdvdcss: add darwin support

pkgs/development/libraries/libdvdcss/default.nix

···
-{ stdenv, fetchurl }:
+{stdenv, fetchurl, IOKit}:
 
 stdenv.mkDerivation rec {
   name = "libdvdcss-${version}";
   version = "1.4.0";
+
+  buildInputs = stdenv.lib.optional stdenv.isDarwin IOKit;
 
   src = fetchurl {
     url = "http://get.videolan.org/libdvdcss/${version}/${name}.tar.bz2";
···
     homepage = http://www.videolan.org/developers/libdvdcss.html;
     description = "A library for decrypting DVDs";
     license = licenses.gpl2;
-    platforms = platforms.linux;
+    platforms = with platforms; linux ++ darwin;
   };
 }

pkgs/top-level/all-packages.nix

···
 
   libdwg = callPackage ../development/libraries/libdwg { };
 
-  libdvdcss = callPackage ../development/libraries/libdvdcss { };
+  libdvdcss = callPackage ../development/libraries/libdvdcss {
+    inherit (darwin) IOKit;
+  };
 
   libdvdnav = callPackage ../development/libraries/libdvdnav { };
   libdvdnav_4_2_1 = callPackage ../development/libraries/libdvdnav/4.2.1.nix {