Fix linking to wxObjectEventFunctor with Clang on Windows

Linking specific applications (sockets/baseserver, base test) resulted in the
following error: undefined reference to `__imp__ZTV20wxObjectEventFunctor'
Fix this by implementing the destructor inside the base library.

src/common/event.cpp

@@ -360,6 +360,14 @@ wxEventFunctor::~wxEventFunctor()
 {
 }
 
+// ----------------------------------------------------------------------------
+// wxObjectEventFunctor
+// ----------------------------------------------------------------------------
+
+wxObjectEventFunctor::~wxObjectEventFunctor()
+{
+}
+
 // ----------------------------------------------------------------------------
 // wxEvent
 // ----------------------------------------------------------------------------