[gtkmm/gtkmm-2-24] configure.ac: Use C++11 if the compiler supports it.

[Murray Cumming <murrayc src gnome org>]

commit 5b8f1294844e3639c6be802dda81fa853511bf30
Author: Murray Cumming <murrayc murrayc com>
Date:   Fri Aug 14 13:50:40 2015 +0200

    configure.ac: Use C++11 if the compiler supports it.
    
    For instance, use --std=c++11 when using g++.
    This will let gtkmm-2.24 build against newer glibmm versions.
    Applications will need to use --std=c++11 too if glibmm is a newer
    version.
    Of course, you should be using gtkmm 3 anyway.

 configure.ac |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index eef1169..6a72d74 100644
--- a/configure.ac
+++ b/configure.ac
@@ -31,7 +31,7 @@ AM_MAINTAINER_MODE
 AC_ARG_VAR([ACLOCAL_FLAGS], [aclocal flags, e.g. -I <macro dir>])
 
 
-MM_PREREQ([0.9.5])
+MM_PREREQ([0.9.8])
 MM_INIT_MODULE([gdkmm-2.4])
 MM_INIT_MODULE([gtkmm-2.4])
 
@@ -44,6 +44,8 @@ MM_CONFIG_DOCTOOL_DIR([docs])
 AC_SUBST([LIBGTKMM_SO_VERSION], [2:0:1])
 
 AC_PROG_CXX
+MM_AX_CXX_COMPILE_STDCXX_11([noext],[optional])
+
 AC_DISABLE_STATIC
 AC_LIBTOOL_WIN32_DLL
 AC_PROG_LIBTOOL