Validate a list structure declarators.
(valid-struct-declor-list structdeclors previous type table ienv) → (mv erp new-structdeclors new-previous return-types new-table)
We validate each structure declarator in turn, threading the data through. Note that the same type (coming from the list of specifiers and qualifiers) is passed to the validation function for each structure declarator, since that type applied to all them (possibly refined, possibly differently, by the structure declarators.