establish installed dependency not in portfile

[Chris Jones]

On 09/10/17 10:18, db wrote:
> On 9 Oct 2017, at 11:16, Chris Jones <jonesc at hep.phy.cam.ac.uk> wrote:
>> Why do you always build from source instead of use the tarballs when available ? Its not entirely reasonable on one hand to complain about build times, and at the same time turn off a feature designed to avoid them...
> 
> No buildbot for 10.8 and libc++.

Ah right, yes.... You could always update your OS, but thats not really 
a fix and you might even have valid reasons for staying on such an old OS.