The most trivial of all derivations. It is more useful than it looks.
Can be used to bind nix expressions (e.g. test suites) to a
derivation, so that `nix-build` does not crap itself.
Change-Id: I61c24d8c129c9505733161207f3c30e820f5b15e
Reviewed-on: https://cl.tvl.fyi/c/depot/+/665
Reviewed-by: tazjin <mail@tazj.in>