Always build with gc assertion code
Include the gc assertion code but allow runtime control on whether the assertions are enabled or not.
Starting November 9th, common-lisp.net's Gitlab instance has implemented a more open account policy, allowing anyone with a GitHub or Google account to create an account on our instance.
At the same time, the login policy has started to require 2-factor authentication (2FA).
See https://mailman.common-lisp.net/pipermail/clo-devel/2018-October/001232.html for discussion.