GTK+ callbacks must have C linkage (patch 1157384)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@32974 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk/gsockgtk.cpp

@@ -21,6 +21,8 @@
 #include "wx/unix/gsockunx.h"
 
 
+extern "C" {
+static
 void _GSocket_GDK_Input(gpointer data,
                         gint source,
                         GdkInputCondition condition)
@@ -32,6 +34,7 @@ void _GSocket_GDK_Input(gpointer data,
   if (condition & GDK_INPUT_WRITE)
     socket->Detected_Write();
 }
+}
 
 bool GSocketGUIFunctionsTableConcrete::CanUseEventLoop()
 {   return true; }