check for wxUSE_MDI which is needed by this code (patch 1656080)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@44463 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

contrib/include/wx/gizmos/dynamicsash.h

@@ -15,6 +15,11 @@
 
 #include "wx/gizmos/gizmos.h"
 
+#if !wxUSE_MDI
+#    error "wxUSE_MDI must be defined for gizmos to compile."
+#endif /* !wxUSE_MDI */
+
+
 /*
 
     wxDynamicSashWindow

contrib/src/gizmos/dynamicsash.cpp

@@ -13,6 +13,8 @@
 // For compilers that support precompilation, includes "wx/wx.h".
 #include "wx/wxprec.h"
 
+#if !wxUSE_MDI
+
 #ifdef __BORLANDC__
     #pragma hdrstop
 #endif
@@ -1469,3 +1471,4 @@ wxDynamicSashReparentEvent::wxDynamicSashReparentEvent(const wxDynamicSashRepare
 
 IMPLEMENT_DYNAMIC_CLASS(wxDynamicSashReparentEvent, wxEvent)
 
+#endif  // !wxUSE_MDI