[Ada] Spurious error on aspect Volatile

This patch modifies the analysis of aspect/pragma Volatile to correct accept
the annotation when it applies to single protected and single task types, and
SPARK_Mode On is in effect.

------------
-- Source --
------------

--  pack.ads

package Pack with SPARK_Mode is
   protected PO_Aspect with Volatile is end;                         --  OK

   protected PO_Pragma is end;
   pragma Volatile (PO_Pragma);                                      --  OK

   task TO_Aspect with Volatile;                                     --  OK

   task TO_Pragma;
   pragma Volatile (TO_Pragma);                                      --  OK
end Pack;

----------------------------
-- Compilation and output --
----------------------------

$ gcc -c pack.ads
$ gcc -c pack.ads -gnatd.F
cannot generate code for file pack.ads (package spec)

2018-05-28  Hristian Kirtchev  <kirtchev@adacore.com>

gcc/ada/

	* sem_prag.adb (Process_Atomic_Independent_Shared_Volatile): Include
	the declarations of single concurrent types because they fall in the
	category of full type and object declarations.

From-SVN: r260820

gcc/ada/ChangeLog

+2018-05-28  Hristian Kirtchev  <kirtchev@adacore.com>
+
+	* sem_prag.adb (Process_Atomic_Independent_Shared_Volatile): Include
+	the declarations of single concurrent types because they fall in the
+	category of full type and object declarations.
+
 2018-05-28  Eric Botcazou  <ebotcazou@adacore.com>
 
 	* repinfo.adb (Compute_Max_Length): Skip _Parent component.

gcc/ada/sem_prag.adb

@@ -7399,9 +7399,11 @@ package body Sem_Prag is
 
          if SPARK_Mode = On
            and then Prag_Id = Pragma_Volatile
-           and then
-             not Nkind_In (Original_Node (Decl), N_Full_Type_Declaration,
-                                                 N_Object_Declaration)
+           and then not Nkind_In (Original_Node (Decl),
+                                  N_Full_Type_Declaration,
+                                  N_Object_Declaration,
+                                  N_Single_Protected_Declaration,
+                                  N_Single_Task_Declaration)
          then
             Error_Pragma_Arg
               ("argument of pragma % must denote a full type or object "