Fix Visual Studio build (nw)

src/emu/debug/debugcpu.h

@@ -37,7 +37,7 @@ const int COMMENT_VERSION               = 1;
 typedef int (*debug_instruction_hook_func)(device_t &device, offs_t curpc);
 
 
-struct xml_data_node;
+class xml_data_node;
 
 
 // ======================> device_debug

src/emu/ioport.h

@@ -661,7 +661,7 @@ class ioport_field;
 struct ioport_field_live;
 class ioport_manager;
 class natural_keyboard;
-struct xml_data_node;
+class xml_data_node;
 class analog_field;
 
 // constructor function pointer

src/emu/render.h

@@ -167,7 +167,7 @@ class device_t;
 class screen_device;
 class render_container;
 class render_manager;
-struct xml_data_node;
+class xml_data_node;
 class render_font;
 struct object_transform;
 class layout_element;