[Ada] Anonymous access types in type declarations in child units

[Arnaud Charlet]

This patch sets properly the scope of an anonymous access type created for
an access to class-wide type declaration in a child unit. Previously the scope
was set to the parent unit, leading to anomalous behavior in the back end.

The following must compile quietly in Ada 2005 mode:

---
package Parent is end;
---
 package Parent.Child is 
    type Employee is abstract tagged  private;
    type myBosses_Type_Array is
      array (Integer range <>) of access Employee'Class;
    type myBosses_Type is access all myBosses_Type_Array;
 private
    type Employee is abstract tagged record 
       myBosses : myBosses_Type;
    end record;
 end;
---

Tested on x86_64-pc-linux-gnu, committed on trunk

2011-09-05  Ed Schonberg  <schonb...@adacore.com>

        * sem_ch3.adb (Access_Definition): If an access type declaration
        appears in a child unit, the scope of whatever anonymous type
        may be generated is the child unit itself.


Index: sem_ch3.adb
===================================================================
--- sem_ch3.adb (revision 178542)
+++ sem_ch3.adb (working copy)
@@ -772,10 +772,16 @@
             Anon_Scope := Scope (Defining_Entity (Related_Nod));
          end if;
 
+         --  For an access type definition, if the current scope is a child
+         --  unit it is the scope of the type.
+
+      elsif Is_Compilation_Unit (Current_Scope) then
+         Anon_Scope := Current_Scope;
+
+      --  For access formals, access components, and access discriminants, the
+      --  scope is that of the enclosing declaration,
+
       else
-         --  For access formals, access components, and access discriminants,
-         --  the scope is that of the enclosing declaration,
-
          Anon_Scope := Scope (Current_Scope);
       end if;