ada: Bug box for expression function with list comprehension

GNAT crashes on an iterator with a filter inside an expression function
that is the completion of an earlier spec.

gcc/ada/

	* freeze.adb (Freeze_Type_Refs): If Node is in N_Has_Etype,
	check that it has had its Etype set, because this can be
	called early for expression functions that are completions.

gcc/ada/freeze.adb

@@ -9137,6 +9137,7 @@ package body Freeze is
          --  that type is not attached to an entity in the construct.
 
          elsif Nkind (Node) in N_Has_Etype
+           and then Present (Etype (Node))
            and then Nkind (Parent (Node)) = N_Iterator_Specification
            and then Node = Name (Parent (Node))
          then