[gtkmm] C++11: gmmproc: GtkObject: Destructor: Use override instead of virtual keyword.

[Murray Cumming <murrayc src gnome org>]

commit 6f34bbea54206efb0e08e42988f534bf7032c14a
Author: Murray Cumming <murrayc murrayc com>
Date:   Thu Dec 24 12:15:34 2015 +0100

    C++11: gmmproc: GtkObject: Destructor: Use override instead of virtual keyword.
    
    This ensures that the base class is really virtual.

 tools/m4/class_gtkobject.m4 |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/tools/m4/class_gtkobject.m4 b/tools/m4/class_gtkobject.m4
index ea14639..8b1f541 100644
--- a/tools/m4/class_gtkobject.m4
+++ b/tools/m4/class_gtkobject.m4
@@ -210,7 +210,7 @@ public:
   __CPPNAME__& operator=(const __CPPNAME__&) = delete;
 
 _IMPORT(SECTION_DTOR_DOCUMENTATION)
-  virtual ~__CPPNAME__`'() noexcept;
+  ~__CPPNAME__`'() noexcept override;
 
 #ifndef DOXYGEN_SHOULD_SKIP_THIS