Add '#include <config.h>' to C++ files in libgui/src * documentation-dockwidget.cc, files-dockwidget.cc, file-editor-tab.cc, file-editor.cc, find-dialog.cc, lexer-octave-gui.cc, main-window.cc, octave-qt-event-listener.cc, qtinfo/parser.cc, settings-dialog.cc, terminal-dockwidget.cc, welcome-wizard.cc, workspace-view.cc: Add '#include <config.h>' as first header file.

--- a/libgui/src/files-dockwidget.cc
+++ b/libgui/src/files-dockwidget.cc
@@ -20,6 +20,10 @@
 
 */
 
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
 #include "resource-manager.h"
 #include "files-dockwidget.h"