ENTRYADDR returns a pointer value that is the address of the first
executed instruction if the entry x is invoked. The entry x must
represent a non-nested procedure.
>>-ENTRYADDR(x)------------------------------------------------><
- x
- Entry reference.
If x is a fetchable entry constant, it must be fetched before ENTRYADDR is executed. However, if x has been released, then ENTRYADDR will return SYSNULL.