Handling C++11

[Marcus Calhoun-Lopez]

At the risk of rehashing a closed topic, I would like to propose a new way of handling C++11 (especially on older systems).
I have opened three tickets that I hope, together, would solve some of the issues raised previously.

[1] https://trac.macports.org/ticket/53194
[2] https://trac.macports.org/ticket/53330
[3] https://trac.macports.org/ticket/53329

I still may not 100% understand libstdc++ vs libc++ vs GCC 5.1 libstdc++, so any suggestions and feedback would be most welcome.

For my own purposes, I would like to both support Octave and Qt on older systems and have the buildbots build them.
Both packages require C++11.
Qt seems to very much require clang to properly interact with the system libraries.

Thank you,
Marcus