Changing default cxx_stdlib to libc++

[Ken Cunningham]

Thank God. 

10.6.8, agree. 

I use clang 3.9 as a good balance between capability and compatability, but might as well sort out how to use clang 5 as that is more consistent w older systems, and I nearly have thread_local working there on 10.6

Ken

Sent from my iPhone

> On Mar 8, 2018, at 9:24 AM, Joshua Root <jmr at macports.org> wrote:
> 
> Code to check C++ stdlib linkage in rev-upgrade is now in master. That
> takes care of the main obstacle to being able to change the default stdlib.
> 
> That leaves a couple of questions:
> 
> Which OS versions can we make the change on? At first glance it looks
> like probably 10.6 through 10.8. 10.5 appears to have a much more
> involved bootstrap process.
> 
> Do we need to make changes to the compiler selection logic? The
> LibcxxOnOlderSystems instructions override the selection in
> macports.conf. Will there be any bootstrap issues for users after the
> switch?
> 
> - Josh