[glibmm] Missing GLIBMM_API for Interface

[Kjell Ahlstedt <kjellahl src gnome org>]

commit bf404d05281b95083705e073d8fb63e513506dd8
Author: Mikhail Titov <mlt gmx us>
Date:   Wed May 6 19:16:15 2015 +0200

    Missing GLIBMM_API for Interface
    
    It is used by Gtk::CellLayout and Gtk::TreeViewColumn. Bug #748719.

 glib/glibmm/interface.h |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/glib/glibmm/interface.h b/glib/glibmm/interface.h
index 0639044..7b453a0 100644
--- a/glib/glibmm/interface.h
+++ b/glib/glibmm/interface.h
@@ -32,7 +32,7 @@ class Interface_Class;
 #endif
 
 // There is no base GInterface struct in Glib, though there is G_TYPE_INTERFACE enum value.
-class Interface : virtual public Glib::ObjectBase
+class GLIBMM_API Interface : virtual public Glib::ObjectBase
 {
 public:
 #ifndef DOXYGEN_SHOULD_SKIP_THIS