It's a bit annoying having to *manually* disable a workflow for forks,
because the scheduled build is a waste of time and also spammy.
On the other hand, having the workflow enabled is in general a good
thing, because it is in fact desirable to test it locally in forks.
The 'build images' workflow runs on a schedule, so will run (and fail)
weekly in every fork.
Don't try to push to docker if docker credentials aren't in repository
secrets.
(A test for that has to be written rather indirectly due to
https://github.com/actions/runner/issues/520)
D lang compilers have an option -release (or similar) which turns off
asserts, contracts, and other runtime type checking. This patch wires
that up to the b_ndebug flag.
Fixes#7082
Eli Schwartz
Daniel Mensinger
Jon Turney
Dylan Baker