[Ada] Compiler fails to reject illegal store of anonymous_access_to_subprogram

[Ada] Compiler fails to reject illegal store of anonymous_access_to_subprogram

GNAT properly rejects an attempt to assign an access_to_subprogram formal
to a local variable, according to accessibiiity rules. This patch forces the
same behavior on the use of such a formal in an object declaration.

Compiling store_anon.adb must yield:

  store_anon.adb:7:35: illegal attempt to store anonymous access to subprogram
  store_anon.adb:7:35: value has deeper accessibility than any master
   (RM 3.10.2 (13))
 store_anon.adb:7:35: use named access type for "P" instead of access parameter

----
package Store_Anon is
   procedure Store (P : not null access procedure);

   procedure Invoke;
end Store_Anon;
----
package body Store_Anon is
   type P_Ptr is access procedure;

   Stored : P_Ptr;

   procedure Store (P : not null access procedure) is
      Illegal : constant P_Ptr := P;
   begin -- Store
      Stored := Illegal;
   end Store;

   procedure Invoke is
      -- Empty
   begin -- Invoke
      Stored.all;
   end Invoke;
end Store_Anon;

2018-05-23  Ed Schonberg  <schonberg@adacore.com>

gcc/ada/

	* sem_ch3.adb (Analyze_Object_Declaration): If expression is an
	anonymous_access_to_ subprogram formal, apply a conversion to force an
	accsssibility check that will fail statically, enforcing 3.10.2 (13).

From-SVN: r260576