Previously user-facing commands would happily start building packages
even if they do not support that system. With this change, all the
user-facing commands reject unsupported packages without going further.
* guix/profiles.scm (profile-derivation): Add #:allow-unsupported-packages?.
Define 'check-supported-packages' and honor #:allow-unsupported-packages?.
* tests/guix-pack.sh, tests/guix-package.sh, tests/guix-shell.sh: Ensure
that unsupported packages are rejected.
* tests/guix-system.sh: Pass "--system=armhf-linux" when attempting to
build gnu/system/examples/asus-c201.tmpl.
The previous behavior was confusing: a warning would be printed and
'guix shell' would go on starting an empty environment.
Reported by Tobias Geerinckx-Rice <me@tobias.gr>.
* guix/scripts/shell.scm (auto-detect-manifest): Change "not loading"
case from warning to error.
* tests/guix-shell.sh: Adjust accordingly.