[Ada] Handling of pragma Predicate

This patch fixes an omission in the processing of pragma Predicate, which
should have the same semantics as the corresponding aspect, which is more
commonly used.

Executing
   gnatmake -q -gnata predicate
   predicate

must yield:

   Even1 violated
   Even2 violated

----
with Text_IO; use Text_IO;
procedure Predicate is
begin
   begin
      declare
         subtype Even1 is Integer;
         pragma Predicate (Even1, Even1 mod 2 = 0);
         X1 : constant Even1 := 1; --  This should fail first
      begin
         null;
      end;
   exception
      when Others => Put_Line ("Even1 violated");
   end;

   begin
      declare
         subtype Even2 is Integer with Predicate => Even2 mod 2 = 0;
         X2 : constant Even2 := 1; --  This should fail later, if reached
      begin
         null;
      end;
   exception
      when Others => Put_Line ("Even2 violated");
   end;
end;

2018-01-11  Ed Schonberg  <schonberg@adacore.com>

gcc/ada/

	* sem_prag.adb (Analyze_Pragma, case Predicate): Indicate that the type
	has a delayed aspect which must be processed at the point the type is
	frozen. This mimics what is done when the predicate is provided by a
	source aspect.

From-SVN: r256495

gcc/ada/ChangeLog

+2018-01-11  Ed Schonberg  <schonberg@adacore.com>
+
+	* sem_prag.adb (Analyze_Pragma, case Predicate): Indicate that the type
+	has a delayed aspect which must be processed at the point the type is
+	frozen. This mimics what is done when the predicate is provided by a
+	source aspect.
+
 2018-01-11  Doug Rupp  <rupp@adacore.com>
 
 	* init.c (vxworks): Add macro checks for __aarch64__.

gcc/ada/sem_prag.adb

@@ -20244,6 +20244,13 @@ package body Sem_Prag is
             --  general Assertion_Policy pragma) to preserve existing warnings.
 
             Set_Has_Predicates (Typ);
+
+            --  Indicate that the pragma must be processed at the point the
+            --  type is frozen, as is done for the corresponding aspect.
+
+            Set_Has_Delayed_Aspects (Typ);
+            Set_Has_Delayed_Freeze (Typ);
+
             Set_Predicates_Ignored (Typ,
               Present (Check_Policy_List)
                 and then