We should configure unconfigured programs before serialising them
(using the Binary ProgramDb instance) in
Distribution.Client.ProjectPlanning.configureCompiler, as otherwise
we can accidentally discard information.

This isn't currently a live bug, because in practice we end up
re-running configuration steps when interfacing with the Cabal library.
However, in the bright future in which we avoid re-configuring things
when building a Cabal package that we already determined when invoking
cabal-install, this starts causing problems.