Sanity check for clash-prelude compilation

[bgamari]

While clash-prelude has -fexpose-all-unfoldings in ghc-options, it is possible for the user to inadvertently configure their tree such to defeat this. In such cases very odd errors will arise since Clash lowers all things lacking unfoldings to Prims. It seems like there are two things that could be done to improve robustness here,

• Explicitly check that all Prims mentioned in a program are known (e.g. have a blackbox)
• Add a sanity check during initialization to verify that some representative bindings from clash-prelude have unfoldings (e.g. Clash.Signal.Bundle.$fBundle(,,))