don't define EMPTY_PARAMETER_VALUE macro without wx prefix, this is an invitation for name clash; instead define wxEMPTY_PARAMETER_VALUE and use it in both variant.h and event.h

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@42993 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/cpp.h

@@ -47,5 +47,11 @@
 /* Create a "unique" name with the given prefix */
 #define wxMAKE_UNIQUE_NAME(text)    wxCONCAT_LINE(text)
 
+/*
+   This macro can be passed as argument to another macro when you don't have
+   anything to pass in fact.
+ */
+#define wxEMPTY_PARAMETER_VALUE /* Fake macro parameter value */
+
 #endif // _WX_CPP_H_