ada: Run-time error with GNAT-LLVM on container aggregate with finalization

When unnesting is enabled, the compiler was failing to copy the At_End_Proc
field from a block statement to the procedure created to replace it when
unnesting of top-level blocks is done.  At run time this could lead to
exceptions due to missing finalization calls.

gcc/ada/

	* exp_ch7.adb (Unnest_Block): Copy the At_End_Proc from the block
	statement to the newly created subprogram body.

gcc/ada/exp_ch7.adb

@@ -8932,7 +8932,8 @@ package body Exp_Ch7 is
               Defining_Unit_Name => Local_Proc),
               Declarations       => Declarations (Decl),
           Handled_Statement_Sequence =>
-            Handled_Statement_Sequence (Decl));
+            Handled_Statement_Sequence (Decl),
+          At_End_Proc                => New_Copy_Tree (At_End_Proc (Decl)));
 
       --  Handlers in the block may contain nested subprograms that require
       --  unnesting.