compilation fix for wxGTK

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@21345 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/apptrait.h

@@ -89,7 +89,9 @@ public:
 
 #if defined(__WXMSW__)
     #include "wx/msw/apptbase.h"
-#else
+#elif defined(__UNIX__)
+    #include "wx/unix/apptbase.h"
+#else // no platform-specific methods to add to wxAppTraits
     typedef 
     // wxAppTraits must be a class because it was forward declared as class
     class WXDLLEXPORT wxAppTraits : public wxAppTraitsBase