Using cxx11 PortGroup on < 10.9

[Mojca Miklavec]

Hi,

Would it be possible to implement a way to use the cxx11 PortGroup
without having to use libc++ as default stdlib? Maybe with an
additional configuration like:
    PortGroup cxx11 1.0
    cxx.require_global_libc++ no
(but with a better keyword of course).

What I have in mind are ports that require C++11, but don't have any
C++ dependencies and thus don't suffer from stdlib incompatibility.

Examples of such ports would be root6, newer versions of clang etc. It
would be handy to have a shortcut, but cxx11 PortGroup alone is a tiny
bit too restrictive.

Mojca