Fix harmless unused parameter warnings in wxDEBUG_LEVEL==0 build.

These warnings were harmless as they concerned the parameters used inside
wxASSERTs only but there were hundreds if not thousands of them in
wx/strvararg.h alone so all the rest of build output was completely lost in
them.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@65046 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk/evtloop.cpp

@@ -91,7 +91,7 @@ void wxGUIEventLoop::WakeUp()
 
 extern "C"
 {
-static gboolean wx_on_channel_event(GIOChannel *channel,
+static gboolean wx_on_channel_event(GIOChannel * WXUNUSED_UNLESS_DEBUG(channel),
                                     GIOCondition condition,
                                     gpointer data)
 {