C++11 flags for jhbuild

[Ian Martin <martin_id vodafone co nz>]

Hi,
I'm trying to build gtkmm with jhbuild.  glibmm fails with a number of 
warnings and errors starting with
> warning: identifier 'decltype' is a keyword in C++11 [-Wc++0x-compat]
>
> /opt/gnome/include/sigc++-2.0/sigc++/functors/functor_trait.h:91:3: 
> warning: identifier 'nullptr' is a keyword in C++11 [-Wc++0x-compat]
>
> /opt/gnome/include/sigc++-2.0/sigc++/functors/functor_trait.h:91:36: 
> error: 'decltype' has not been declared
>
> /opt/gnome/include/sigc++-2.0/sigc++/functors/functor_trait.h:96:44: 
> error: 'nullptr' was not declared in this scope
>      = sizeof(check(static_cast<T_functor*>(nullptr))) == sizeof(int)
I'm guessing this means I need to enable C++11 within jhbuild.  Do I do 
this in my .jhbuildrc or should this be a compiler flag added within the 
glibmm configure.ac?

Ian