SDL2_{gfx,mixer,net,ttf}: fix Darwin build

pkgs/development/libraries/SDL2_gfx/default.nix

···
-{ stdenv, fetchurl, SDL2 }:
+{ stdenv, darwin, fetchurl, SDL2 }:
 
 stdenv.mkDerivation rec {
   name = "SDL2_gfx-${version}";
···
     url = "mirror://sourceforge/sdl2gfx/${name}.tar.gz";
     sha256 = "16jrijzdp095qf416zvj9gs2fqqn6zkyvlxs5xqybd0ip37cp6yn";
   };
+
+  nativeBuildInputs = stdenv.lib.optional stdenv.isDarwin darwin.libobjc;
 
   buildInputs = [ SDL2 ];
 
···
     license = licenses.zlib;
 
     maintainers = with maintainers; [ bjg ];
-    platforms = platforms.linux;
+    platforms = platforms.unix;
   };
 }

pkgs/development/libraries/SDL2_mixer/default.nix

···
 { stdenv, lib, fetchurl, autoreconfHook, pkgconfig, which
 , SDL2, libogg, libvorbis, smpeg2, flac, libmodplug
+, CoreServices, AudioUnit, AudioToolbox
 , enableNativeMidi ? false, fluidsynth ? null }:
 
 stdenv.mkDerivation rec {
···
 
   nativeBuildInputs = [ autoreconfHook pkgconfig which ];
 
+  buildInputs = stdenv.lib.optionals stdenv.isDarwin [ CoreServices AudioUnit AudioToolbox ];
+
   propagatedBuildInputs = [ SDL2 libogg libvorbis fluidsynth smpeg2 flac libmodplug ];
 
   configureFlags = [ "--disable-music-ogg-shared" ]
···
 
   meta = with stdenv.lib; {
     description = "SDL multi-channel audio mixer library";
-    platforms = platforms.linux;
+    platforms = platforms.unix;
     homepage = https://www.libsdl.org/projects/SDL_mixer/;
     maintainers = with maintainers; [ MP2E ];
     license = licenses.zlib;

pkgs/development/libraries/SDL2_net/default.nix

···
-{ stdenv, fetchurl, SDL2 }:
+{ stdenv, darwin, fetchurl, SDL2 }:
 
 stdenv.mkDerivation rec {
   name = "SDL2_net-${version}";
···
     sha256 = "08cxc1bicmyk89kiks7izw1rlx5ng5n6xpy8fy0zxni3b9z8mkhm";
   };
 
+  nativeBuildInputs = stdenv.lib.optional stdenv.isDarwin darwin.libobjc;
+
   propagatedBuildInputs = [ SDL2 ];
 
   meta = with stdenv.lib; {
···
     homepage = https://www.libsdl.org/projects/SDL_net;
     license = licenses.zlib;
     maintainers = with maintainers; [ MP2E ];
-    platforms = platforms.linux;
+    platforms = platforms.unix;
   };
 }

pkgs/development/libraries/SDL2_ttf/default.nix

···
-{ stdenv, fetchurl, SDL2, freetype, mesa_noglu }:
+{ stdenv, darwin, fetchurl, SDL2, freetype, mesa_noglu }:
 
 stdenv.mkDerivation rec {
   name = "SDL2_ttf-${version}";
···
     sha256 = "0xljwcpvd2knrjdfag5b257xqayplz55mqlszrqp0kpnphh5xnrl";
   };
 
+  nativeBuildInputs = stdenv.lib.optional stdenv.isDarwin darwin.libobjc;
+
   buildInputs = [ SDL2 freetype mesa_noglu ];
 
   meta = with stdenv.lib; {
     description = "SDL TrueType library";
-    platforms = platforms.linux;
+    platforms = platforms.unix;
     license = licenses.zlib;
     homepage = https://www.libsdl.org/projects/SDL_ttf/;
   };

pkgs/development/libraries/smpeg2/default.nix

···
-{ stdenv, fetchsvn, autoconf, automake, libtool, m4, pkgconfig, makeWrapper, SDL2 }:
+{ stdenv, darwin, fetchsvn, autoconf, automake, libtool, m4, pkgconfig, makeWrapper, SDL2 }:
 
 stdenv.mkDerivation rec {
   name = "smpeg2-svn${version}";
···
     ./sdl2.patch
   ];
 
-  nativeBuildInputs = [ autoconf automake pkgconfig makeWrapper ];
+  nativeBuildInputs = [ autoconf automake pkgconfig makeWrapper ]
+    ++ stdenv.lib.optional stdenv.isDarwin darwin.libobjc;
 
   buildInputs = [ SDL2 ];
 
···
     homepage = http://icculus.org/smpeg/;
     description = "SDL2 MPEG Player Library";
     license = licenses.lgpl2;
-    platforms = platforms.linux;
+    platforms = platforms.unix;
     maintainers = with maintainers; [ orivej ];
   };
 }

pkgs/top-level/all-packages.nix

···
     inherit (darwin.apple_sdk.frameworks) Foundation;
   };
 
-  SDL2_mixer = callPackage ../development/libraries/SDL2_mixer { };
+  SDL2_mixer = callPackage ../development/libraries/SDL2_mixer {
+    inherit (darwin.apple_sdk.frameworks) CoreServices AudioUnit AudioToolbox;
+  };
 
   SDL2_net = callPackage ../development/libraries/SDL2_net { };