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

[Murray Cumming <murrayc src gnome org>]

commit 62f62d07372bbd13a44411e8866831610e5cdaef
Author: Murray Cumming <murrayc murrayc com>
Date:   Fri Jul 26 13:17:16 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 e2ae574..95f883f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -115,7 +115,7 @@ GLIBMM_ARG_ENABLE_DEBUG_REFCOUNTING
 MM_ARG_ENABLE_WARNINGS([GLIBMM_WXXFLAGS],
                        [-Wall],
                        [-pedantic -Wall -Wextra -Wformat-security -Wno-long-long],
-                       [G])
+                       [G SIGCXX])
 
 # Offer the ability to omit some API from the library,
 # to reduce the code size: