Must define a symbol to test its value

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@42348 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/generic/caret.h

@@ -18,6 +18,8 @@
 
 #if wxHAS_NATIVE_OVERLAY
     #define wxHAS_CARET_USING_OVERLAYS 1
+#else
+    #define wxHAS_CARET_USING_OVERLAYS 0
 #endif
 
 class WXDLLIMPEXP_CORE wxCaret;