Looks like several functions removed between gtk+-2.3.0 and 2.3.1:

 g++ -DHAVE_CONFIG_H -DG_LOG_DOMAIN=\"gtkmm\" -I../../gtk
-I../../../gtkmm-2.3.0/gtk -I../../pango -I../../../gtkmm-2.3.0/pango
-I../../atk -I../../../gtkmm-2.3.0/atk -I../../gdk
-I../../../gtkmm-2.3.0/gdk -I../../gtk -I../../../gtkmm-2.3.0/gtk
-I/usr/include/glibmm-2.3 -I/usr/lib/glibmm-2.3/include
-I/usr/lib/sigc++-1.2/include -I/usr/include/sigc++-1.2
-I/usr/include/glib-2.0 -I/usr/lib/glib-2.0/include -I/usr/include/gtk-2.0
-I/usr/lib/gtk-2.0/include -I/usr/include/atk-1.0 -I/usr/X11R6/include
-I/usr/include/pango-1.0 -I/usr/include/freetype2 -g -O2 -Wall -c
../../../gtkmm-2.3.0/gtk/gtkmm/toolitem.cc -Wp,-MD,.deps/toolitem.TPlo 
-fPIC -DPIC -o .libs/toolitem.o
../../../gtkmm-2.3.0/gtk/gtkmm/toolitem.cc: In method `void
Gtk::ToolItem::set_pack_end(bool = true)':
../../../gtkmm-2.3.0/gtk/gtkmm/toolitem.cc:293: implicit declaration of
function `int Gtk::gtk_tool_item_set_pack_end(...)'
../../../gtkmm-2.3.0/gtk/gtkmm/toolitem.cc: In method `bool
Gtk::ToolItem::get_pack_end() const':
../../../gtkmm-2.3.0/gtk/gtkmm/toolitem.cc:298: implicit declaration of
function `int Gtk::gtk_tool_item_get_pack_end(...)'
make[1]: *** [toolitem.lo] Error 1
make[1]: Leaving directory `/usr/src/gtkmm/gtkmm-2.3.0-build/gtk/gtkmm'
make: *** [all-recursive] Error 1