Return true if mdata should be preserved.
Right now, we don't preserve any MData, but this may
change in the future when we add support for debugging information
Return true if e is a lcCast application.
Store information about casesOn declarations.
We treat them uniformly in the code generator.
List of types that have builtin runtime support
Return true iff declName is the name of a type with builtin support in the runtime.