The new class 'Gtkmm2ext::EventBoxExt' needs to be exportable when building with MSVC

(previously the c'tor was private and nothing was getting exported anyway)

libs/gtkmm2ext/eventboxext.cc

@@ -0,0 +1,25 @@
+/*
+ * Copyright (C) 2017 Robin Gareus <robin@gareus.org>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ */
+
+#include "gtkmm2ext/eventboxext.h"
+
+using namespace Gtkmm2ext;
+
+EventBoxExt::EventBoxExt ()
+{
+}

libs/gtkmm2ext/gtkmm2ext/eventboxext.h

@@ -28,6 +28,7 @@ namespace Gtkmm2ext {
 class LIBGTKMM2EXT_API EventBoxExt : public Gtk::EventBox
 {
 public:
+	EventBoxExt ();
 	virtual ~EventBoxExt () {}
 
 protected: