Fix empty Cycles render devices panel showing in preferences on macOS

There is no GPU rendering support on macOS, so showing the panel only adds
confusion. Also hide the panels in builds without Cycles.

release/scripts/startup/bl_ui/space_userpref.py

@@ -575,6 +575,12 @@ class USERPREF_PT_system_sound(SystemPanel, CenterAlignMixIn, Panel):
 class USERPREF_PT_system_cycles_devices(SystemPanel, CenterAlignMixIn, Panel):
     bl_label = "Cycles Render Devices"
 
+    @classmethod
+    def poll(cls, context):
+        # No GPU rendering on macOS currently.
+        import sys
+        return bpy.app.build_options.cycles and sys.platform != "darwin"
+
     def draw_centered(self, context, layout):
         prefs = context.preferences