* sem_ch6.adb (Check_Access_Invariants): Test whether an
invariant procedure is empty before generating a call to it.
(Has_Enabled_Predicate): New routine.
(Has_Null_Body): New routine.
(Process_PPCs): Test whether an invariant procedure is
empty before generating a call to it. Test whether predicates are
enabled for a particular type before generating a predicate call.
* sem_util.ads, sem_util.adb (Find_Pragma): New routine.