Allow comparing all pointer types to nil

gcc/elna-tree.cc

@@ -23,6 +23,12 @@ namespace gcc
         return TREE_CODE(type) == POINTER_TYPE;
     }
 
+    bool are_compatible_pointers(tree lhs, tree rhs)
+    {
+        return (lhs == null_pointer_node || rhs == null_pointer_node)
+            && is_pointer_type(TREE_TYPE(lhs)) && is_pointer_type(TREE_TYPE(rhs));
+    }
+
     tree tree_chain_base::head()
     {
         return first;