[gtkmm] configure.ac: Avoid deprecated libsigc++ API.

[Murray Cumming <murrayc src gnome org>]

commit 23f724918bd74a7c6f1a2a6ba5056dd147fda758
Author: Murray Cumming <murrayc murrayc com>
Date:   Fri Jul 26 13:17:55 2013 +0200

    configure.ac: Avoid deprecated libsigc++ API.

 configure.ac |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 161c059..cf754b3 100644
--- a/configure.ac
+++ b/configure.ac
@@ -130,7 +130,7 @@ AC_CHECK_FUNCS([flockfile funlockfile getc_unlocked mkfifo])
 MM_ARG_ENABLE_WARNINGS([GTKMM_WXXFLAGS],
                        [-Wall],
                        [-pedantic -Wall -Wextra -Wformat-security -Wno-long-long -DGSEAL_ENABLE],
-                       [G PANGO ATK GDK GDK_PIXBUF GTK GLIBMM ATKMM PANGOMM CAIROMM])
+                       [G PANGO ATK GDK GDK_PIXBUF GTK GLIBMM ATKMM PANGOMM CAIROMM SIGCXX])
 
 AC_CONFIG_FILES([Makefile
                  tools/Makefile