[gtkmm] Link to the glibmm-2.52 version of glibmm_generate_extra_defs.

[Murray Cumming <murrayc src gnome org>]

commit b8bc3f349b2253d3e2a9dc8a755e48782d5d9ed6
Author: Murray Cumming <murrayc murrayc com>
Date:   Tue Nov 15 21:18:59 2016 +0100

    Link to the glibmm-2.52 version of glibmm_generate_extra_defs.

 tools/Makefile.am |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/tools/Makefile.am b/tools/Makefile.am
index 07d99b4..295aeaf 100644
--- a/tools/Makefile.am
+++ b/tools/Makefile.am
@@ -27,11 +27,11 @@ noinst_PROGRAMS = extra_defs_gen/generate_defs_gdk \
                   extra_defs_gen/generate_defs_gtk
 
 extra_defs_gen_generate_defs_gdk_SOURCES = extra_defs_gen/generate_defs_gdk.cc
-extra_defs_gen_generate_defs_gdk_LDADD   = $(GTKMM_LIBS) -lglibmm_generate_extra_defs-2.4
+extra_defs_gen_generate_defs_gdk_LDADD   = $(GTKMM_LIBS) -lglibmm_generate_extra_defs-2.52
 extra_defs_gen_generate_defs_gdk_LDFLAGS = -no-undefined -avoid-version
 
 extra_defs_gen_generate_defs_gtk_SOURCES = extra_defs_gen/generate_defs_gtk.cc
-extra_defs_gen_generate_defs_gtk_LDADD   = $(GTKMM_LIBS) -lglibmm_generate_extra_defs-2.4
+extra_defs_gen_generate_defs_gtk_LDADD   = $(GTKMM_LIBS) -lglibmm_generate_extra_defs-2.52
 extra_defs_gen_generate_defs_gtk_LDFLAGS = -no-undefined -avoid-version
 
 AM_CPPFLAGS = -I$(top_builddir) $(GTHREAD_CFLAGS) $(GTKMM_CFLAGS)