Fix UnbindFromHandler() test compilation with C++98

Can't declare classes inside the function as they must have external linkage
to be usable with Bind().

Fixes the build after 99d9a81e28, see #17229.

tests/events/evthandler.cpp

@@ -462,46 +462,49 @@ void EvtHandlerTestCase::InvalidBind()
 #endif
 }
 
+// Helpers for UnbindFromHandler() test, have to be declared outside of the
+// function in C++98.
+struct Handler1
+{
+    void OnDontCall(MyEvent&)
+    {
+        // Although this handler is bound, the second one below is bound
+        // later and so will be called first and will disconnect this one
+        // before it has a chance to be called.
+        CPPUNIT_FAIL("shouldn't be called");
+    }
+};
+
+class Handler2
+{
+public:
+    Handler2(MyHandler& handler, Handler1& h1)
+        : m_handler(handler),
+          m_h1(h1)
+    {
+    }
+
+    void OnUnbind(MyEvent& e)
+    {
+        m_handler.Unbind(MyEventType, &Handler1::OnDontCall, &m_h1);
+
+        // Check that the now disconnected first handler is not executed.
+        e.Skip();
+    }
+
+private:
+    MyHandler& m_handler;
+    Handler1& m_h1;
+
+    wxDECLARE_NO_COPY_CLASS(Handler2);
+};
+
 void EvtHandlerTestCase::UnbindFromHandler()
 {
-    struct Handler1
-    {
-        void OnDontCall(MyEvent&)
-        {
-            // Although this handler is bound, the second one below is bound
-            // later and so will be called first and will disconnect this one
-            // before it has a chance to be called.
-            CPPUNIT_FAIL("shouldn't be called");
-        }
-    } h1;
-
+    Handler1 h1;
     handler.Bind(MyEventType, &Handler1::OnDontCall, &h1);
 
-    class Handler2
-    {
-    public:
-        Handler2(MyHandler& handler, Handler1& h1)
-        {
-            m_handler = &handler;
-            m_h1 = &h1;
-        }
-
-        void OnUnbind(MyEvent& e)
-        {
-            m_handler->Unbind(MyEventType, &Handler1::OnDontCall, m_h1);
-
-            // Check that the now disconnected first handler is not executed.
-            e.Skip();
-        }
-
-    private:
-        // Use pointers instead of references just to avoid warnings about the
-        // class being non-copyable even though these pointers don't change and
-        // are non-NULL.
-        MyHandler* m_handler;
-        Handler1* m_h1;
-    } h2(handler, h1);
-
+    Handler2 h2(handler, h1);
     handler.Bind(MyEventType, &Handler2::OnUnbind, &h2);
 
     handler.ProcessEvent(e);