defaultIconTheme: Enable darwin support

pkgs/data/icons/hicolor-icon-theme/default.nix

@@ -13,6 +13,6 @@ stdenv.mkDerivation rec {
   meta = {
     description = "Default fallback theme used by implementations of the icon theme specification";
     homepage = http://icon-theme.freedesktop.org/releases/;
-    platforms = stdenv.lib.platforms.linux;
+    platforms = with stdenv.lib.platforms; linux ++ darwin;
   };
 }

pkgs/desktops/gnome-3/3.22/core/adwaita-icon-theme/default.nix

@@ -15,7 +15,7 @@ stdenv.mkDerivation rec {
   postInstall = '' rm -rf "$out/locale" '';
 
   meta = with stdenv.lib; {
-    platforms = platforms.linux;
+    platforms = with platforms; linux ++ darwin;
     maintainers = gnome3.maintainers;
   };
 }

pkgs/development/tools/misc/icon-naming-utils/default.nix

@@ -19,6 +19,6 @@ stdenv.mkDerivation rec {
 
   meta = with stdenv.lib; {
     homepage = http://tango.freedesktop.org/Standard_Icon_Naming_Specification;
-    platforms = platforms.linux;
+    platforms = with platforms; linux ++ darwin;
   };
 }