cxx11 portgroup: C++11, C++14, C++17

[Ken Cunningham]

By providing a current clang, like 5.0, all these are covered I believe. 

The PG is really misnamed....should be "modern compiler" PG or similar. 

K

Sent from my iPhone

> On Feb 4, 2018, at 6:56 PM, Ryan Schmidt <ryandesign at macports.org> wrote:
> 
> The cxx11 portgroup is fine for C++11, but what do we want to do about C++14, C++17, and future versions?
>