establish installed dependency not in portfile

[Chris Jones]

On 08/10/17 20:46, db wrote:
> On 8 Oct 2017, at 21:19, Ryan Schmidt <ryandesign at macports.org> wrote:
>> On Oct 8, 2017, at 05:17, db wrote:
>>> Since py27-numpy is the only port installed requiring gcc7, I rather choose gcc6 which is used by many others instead.
>> You can do that, but since gcc7 is the latest stable version of gcc, ports that currently use gcc6 by default will be updated over time to use gcc7 instead.
> 
> Until then, since I always build from source, I rather save CPU time. Speaking of which, getting back to my first post, is there any way to query the build time from the buildbots? It'd be useful to estimate when to do an update.

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...