Switching cxx_stdlib for C++11 on legacy macOS

[Ken Cunningham]

> As I understand it, to support C++11 the only way is to switch to
> libc++. 

That was true a year ago, but is no longer true.

The cxx11 1.1 PortGroup offers c++11 support for all systems back to Tiger with no change in the standard library.

There is no good reason to change to libc++ on those systems now, other than consistency with systems 10.9+ (which I did advocate for at the time but in the end that approach was more complicated and lost out).


K