-;;; If there are arguments, MULTIPLE-VALUE-CALL turns into an
-;;; MV-COMBINATION.
-;;;
-;;; If there are no arguments, then we convert to a normal
-;;; combination, ensuring that a MV-COMBINATION always has at least
-;;; one argument. This can be regarded as an optimization, but it is
-;;; more important for simplifying compilation of MV-COMBINATIONS.