Fix wxAUI build with wxUSE_MDI==0

Include wx/frame.h explicitly as it's not included by wx/aui/tabmdi.h in
this case.

Closes #18291.

src/aui/auibook.cpp

@@ -26,6 +26,7 @@
     #include "wx/settings.h"
     #include "wx/dcclient.h"
     #include "wx/dcmemory.h"
+    #include "wx/frame.h"
 #endif
 
 #include "wx/aui/tabmdi.h"