quartz: fix build on 10.6 and below

It is not possible to successfully build GTK+ on OS X 10.6 and below
since NSFullScreenWindowMask is only available starting with 10.7. Add
ifdef guards around setStyleMask: in order to allow it to build on
earlier OS X releases.

https://bugzilla.gnome.org/show_bug.cgi?id=737561

gdk/quartz/GdkQuartzNSWindow.c

@@ -654,6 +654,8 @@ update_context_from_dragging_info (id <NSDraggingInfo> sender)
   _gdk_quartz_drag_source_context = NULL;
 }
 
+#ifdef AVAILABLE_MAC_OS_X_VERSION_10_7_AND_LATER
+
 - (void)setStyleMask:(NSUInteger)styleMask
 {
   gboolean was_fullscreen;
@@ -669,4 +671,6 @@ update_context_from_dragging_info (id <NSDraggingInfo> sender)
     _gdk_quartz_window_update_fullscreen_state ([[self contentView] gdkWindow]);
 }
 
+#endif
+
 @end

gdk/quartz/GdkQuartzNSWindow.h

@@ -42,7 +42,10 @@
 -(BOOL)trackManualResize;
 -(void)showAndMakeKey:(BOOL)makeKey;
 -(void)hide;
+
+#ifdef AVAILABLE_MAC_OS_X_VERSION_10_7_AND_LATER
 -(void)setStyleMask:(NSUInteger)styleMask;
+#endif
 
 @end