Use value_at_non_lval in get_call_return_value

get_call_return_value can handle RETURN_VALUE_STRUCT_CONVENTION,
because the call is completely managed by gdb.  However, it does not
handle variably-sized types correctly.  The simplest way to fix this
is to use value_at_non_lval, which does type resolution.

Author: tromey

gdb/infcall.c

@@ -476,12 +476,7 @@ get_call_return_value (struct call_return_meta_info *ri)
 	  push_thread_stack_temporary (thr, retval);
 	}
       else
-	{
-	  retval = allocate_value (ri->value_type);
-	  read_value_memory (retval, 0, 1, ri->struct_addr,
-			     value_contents_raw (retval).data (),
-			     ri->value_type->length ());
-	}
+	retval = value_at_non_lval (ri->value_type, ri->struct_addr);
     }
   else
     {