Fix hidden symbol runtime problem

src/apt.cpp

@@ -927,6 +927,8 @@ KURL AptProtocol::buildURL( const KURL& query ) const
 *
 */
 
+extern "C" { KDE_EXPORT int kdemain(int argc, char **argv); }
+
 extern "C" {
   int kdemain( int argc, char **argv ) {
     TDEInstance instance( "tdeio_apt" );