add wxUSE_WEAKREF (modified partially applied patch 1870445)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@51614 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/chkconf.h

@@ -291,6 +291,14 @@
 #   endif
 #endif /* wxUSE_VARIANT */
 
+#ifndef wxUSE_WEAKREF
+#   ifdef wxABORT_ON_CONFIG_ERROR
+#       error "wxUSE_WEAKREF must be defined."
+#   else
+#       define wxUSE_WEAKREF 0
+#   endif
+#endif /* wxUSE_WEAKREF */
+
 /*
    Section 1b: all these tests are for GUI only.