Support (case-lambda) tail recursion

[etaoins]

R7RS requires (case-lambda) to be tail recursive. However, our new (case-lambda) generation has a few issues:

• We always generate (case-lambda) with the same signature as TopProcedureType regardless of the types of the clause lambdas. This usually means we'll need to allocate a multiple values list at return which prevents tail recursion. It also uses the C calling convention which isn't required to support tail calls.
• Clause lambdas don't have their recursive self values passed so they need to call through a cell which isn't supported
• We never produce fixed arguments for (case-lambda)'s signature which means the a tail caller will always need to allocate a rest argument list. This doesn't prevent tail recursion but makes it potentially expensive