GitLab

The old ones went down. Hopefully somebody will approve these going on
downloads.haskell.org someday instead.

Got hash from https://dhall-lang.org/, for what it's worth.

This image now lives in debian.dhall

It was EOL'd in July 2018 and we no longer have a compatible LLVM
bindist for it.

To allow testing of hadrian build.

As noted in ghc#15230, we must disable the systemd nsswitch provider
on RedHat-based distributions.

There are no binary distributions for LLVM 10 on Debian 9.

Previously files would end up in the root user's store, which is
inaccessible to others.

Fixes escaping of ENVs.

This is a major refactoring and consolidation of the Docker image
generation logic. It eliminates a great deal of repetition, resolves
several inconsistencies, and makes the Docker images significantly more
maintainable.

We now expose the following environment variables to ensure that tools
are specified explicitly:

 * CABAL
 * GHC
 * OPT
 * LLC
 * HAPPY
 * ALEX
 * HSCOLOUR

`configure` will pick these up.