python BUILDLINK_DEPMETHOD workaround

[Jonathan Perkin <jperkin%pkgsrc.org@localhost>]

I thought we were in careful mode so was going to hold off on this, but 
judging by some of the commits still going in I guess it's ok.

py-pybind11's insistence on DEPMETHOD=build is still causing problems, 
and the daily bulk builds have shown graphics/py-matplotlib as a top 
breakage for a long time now.

This patch "fixes" it:

  https://github.com/TritonDataCenter/pkgsrc/commit/c875baf1

I've tested it in a bulk build, and have not observed any regressions.

--
Jonathan Perkin                    pkgsrc.smartos.org
Open Source Complete Cloud   www.tritondatacenter.com