The https://github.com/mitls/hacl-c repo was deleted.
Getting the new upstream (https://github.com/project-everest/hacl-star)
to work nicely as a package requires some non-trivial work and in the
meantime all CI jobs will fail.
As a short-term solution, switch the upstream to a backup version of
the original repository.
Prepare for handling pkg state with files. So it requires having the
path defined before declaring targets. In addition, it cleans up the
old git-download target.
