* ali.adb: Document the remaining letters available for ALI lines.
(Scan_ALI): A with clause is internal when it is encoded on a 'Z' line.
* ali.ads: Update type With_Record. Field
Implicit_With_From_Instantiation is no longer in use. Add field
Implicit_With.
* csinfo.adb (CSinfo): Remove the setup for attribute
Implicit_With_From_Instantiation.
* lib-writ.adb (Collect_Withs): Correct the logic which marks a unit as
either implicitly or explicitly withed.
(Is_Implicit_With_Clause): New routine.
(Write_ALI): Rename array Implicit_With to Has_Implicit_With to avoid
confusion with the with clause attribute by the same name.
(Write_With_Lines): Update the emission of 'W', 'Y', and 'Z' headers.
* rtsfind.adb (Maybe_Add_With): Code cleanup.
* sem_ch8.adb (Present_System_Aux): Code cleanup.
* sem_ch10.adb (Expand_With_Clause): Mark the with clause as generated
for a parent unit.
(Implicit_With_On_Parent): Mark the with clause as generated for a
parent unit.
* sem_ch12.adb (Inherit_Context): With clauses inherited by an
instantiation are no longer marked as Implicit_With_From_Instantiation
because they are already marked as implicit.
* sem_elab.adb (Ensure_Prior_Elaboration_Static): Remove the kludge
which marks implicit with clauses as related to an instantiation.
* sinfo.adb (Implicit_With_From_Instantiation): Removed.
(Parent_With): New routine.
(Set_Implicit_With_From_Instantiation): Removed.
(Set_Parent_With): New routine.
* sinfo.ads: Update the documentation of attribute Implicit_With.
Remove attribute Implicit_With_From_Instantiation along with
occurrences in nodes. Add attribute Parent_With along with occurrences
in nodes.
(Implicit_With_From_Instantiation): Removed along with pragma Inline.
(Parent_With): New routine along with pragma Inline.
(Set_Implicit_With_From_Instantiation): Removed along with pragma Inline.
(Set_Parent_With): New routine along with pragma Inline.