ada: Compiler fails on unchecked deallocation for constrained protected subtype

The compiler fails with an error or Assert_Failure when calling
an instantiation of Unchecked_Deallocation that has been instantiated
with a constrained subtype of a discriminated protected type.

gcc/ada/ChangeLog:

	* sem_ch3.adb (Constrain_Corresponding_Record): Inherit Class_Wide_Type on the
	created constrained subtype.
diff --git a/gcc/ada/sem_ch3.adb b/gcc/ada/sem_ch3.adb
index 8246e6c..794e420 100644
--- a/gcc/ada/sem_ch3.adb
+++ b/gcc/ada/sem_ch3.adb
@@ -14601,6 +14601,7 @@
       Set_Etype             (T_Sub, Corr_Rec);
       Set_Has_Discriminants (T_Sub, Has_Discriminants (Prot_Subt));
       Set_Is_Tagged_Type    (T_Sub, Is_Tagged_Type (Corr_Rec));
+      Set_Class_Wide_Type   (T_Sub, Class_Wide_Type (Corr_Rec));
       Set_Is_Constrained    (T_Sub, True);
       Set_First_Entity      (T_Sub, First_Entity (Corr_Rec));
       Set_Last_Entity       (T_Sub, Last_Entity  (Corr_Rec));