* sem_ch10.adb (Is_Ancestor_Unit): Make global, for use elsewhere.
(Install_Private_with_Clauses): if clause is private and limited,
do not install the limited view if the library unit is an ancestor
of the unit being compiled. This unusual configuration occurs
when compiling a unit DDP, when an ancestor P of DDP has a
private limited with clause on a descendant of P that is itself
an ancestor of DDP.