Validate an abstract declarator.
(valid-absdeclor absdeclor type table ienv) → (mv erp new-absdeclor new-type return-types new-table)
This is fairly similar to valid-declor (see that function's documentation), but since the declarator is abstract, there is no identifier being declared to return. Furthermore, there is no flag for function definitions, since a function definition uses a declarator, not an abstract declarator.