establish installed dependency not in portfile

[Ken Cunningham]

you (and I) build everthing from source because of our libc++ setting on older systems.

I used to think that was bad, but now I think it has led me to learn far more than I otherwise would have.

There are buildbots for almost every system running away as we speak. 

> On Oct 9, 2017, at 7:23 AM, db <iamsudo at gmail.com> wrote:
> 
>> On 9 Oct 2017, at 16:00, Rainer Müller <raimue at macports.org> wrote:
>>> On 2017-10-09 15:21, db wrote:
>>> There are still no binaries for all ports for the previous supported OS releases, i.e., 10.11 and 10.12.
>> Due to license conflicts, we cannot distribute binaries for all ports.
> 
> I rather thought that the buildbots didn't finished all binaries for those OS versions yet.