[Ada] Spurious visibility error on aspect in generic unit

This patch fixes a spurious visiblity error on an instantiation of a generic
package that contains a type declaration with an aspect specification for
an aspect that must be delayed (i.e. an aspect whose value may be specified
at a later point).

The package g.ads must compile quietly:

----
with S;
generic
package G
is
   type Buffer_Type is record
      Data       : Integer;
   end record;

   package Buffer is new S (Buffer_Type => Buffer_Type);
end G;
----
generic
   type Buffer_Type is private;
package S
is
   Page_Size : constant := 4096;

   type Reader_Type is limited record
      Data   : Buffer_Type;
   end record
     with
        Alignment => Page_Size; -- Using a constant does not work
--      Alignment => 4096;      -- Using a number works

-- for Reader_Type'Alignment use Page_Size; -- so does an attribute.
   pragma Compile_Time_Error (Reader_Type'Size /= 12345, "Ooops");
   -- Note: We set 'Alignment and check for 'Size.
end S;

2018-05-22  Ed Schonberg  <schonberg@adacore.com>

gcc/ada/

	* freeze.adb (Freeze_Entity): When analyzing delayed aspects of an
	entity E within a generic unit, indicate that there are no remaining
	delayed aspects after invoking Analyze_Aspects_At_Freeze_Point. The
	entity E is not frozen yet but the aspects should not be reanalyzed at
	the freeze point, which may be outside of the generic and may not have
	the proper visibility.

From-SVN: r260516

gcc/ada/ChangeLog

+2018-05-22  Ed Schonberg  <schonberg@adacore.com>
+
+	* freeze.adb (Freeze_Entity): When analyzing delayed aspects of an
+	entity E within a generic unit, indicate that there are no remaining
+	delayed aspects after invoking Analyze_Aspects_At_Freeze_Point. The
+	entity E is not frozen yet but the aspects should not be reanalyzed at
+	the freeze point, which may be outside of the generic and may not have
+	the proper visibility.
+
 2018-05-22  Bob Duff  <duff@adacore.com>
 
 	* doc/gnat_ugn/gnat_utility_programs.rst: Add documentation for

gcc/ada/freeze.adb

@@ -5167,11 +5167,14 @@ package body Freeze is
       --  be frozen in the proper scope after the current generic is analyzed.
       --  However, aspects must be analyzed because they may be queried later
       --  within the generic itself, and the corresponding pragma or attribute
-      --  definition has not been analyzed yet.
+      --  definition has not been analyzed yet. After this, indicate that the
+      --  entity has no further delayed aspects, to prevent a later aspect
+      --  analysis out of the scope of the generic.
 
       elsif Inside_A_Generic and then External_Ref_In_Generic (Test_E) then
          if Has_Delayed_Aspects (E) then
             Analyze_Aspects_At_Freeze_Point (E);
+            Set_Has_Delayed_Aspects (E, False);
          end if;
 
          Result := No_List;