Subject: Boost 1.60.0 is not bit-reproducible

From: Leo Famulari <[email-masked]>
Date: Wed, 05 Dec 2018 15:10:26 -0500

As of today, with Boost 1.68.0, it seems that Boost builds reproducibly.

It works with --rounds=3, and `guix challenge` against Hydra and Berlin succeeds.