trans.c (assoc_to_constructor): Make sure Corresponding_Discriminant is only called on discriminants.

2017-05-02  Eric Botcazou  <ebotcazou@adacore.com>

	* gcc-interface/trans.c (assoc_to_constructor): Make sure
	Corresponding_Discriminant is only called on discriminants.
	Skip the saving of the result only for them.
	(gnat_to_gnu) <N_Selected_Component>: Likewise.
	<N_Unchecked_Type_Conversion>: Translate the result type first.
	(gigi): Set TREE_NOTHROW on Begin_Handler.
	(stmt_list_cannot_raise_p): New predicate.
	(Exception_Handler_to_gnu_gcc): Emit a simple final call instead of
	a cleanup if the statements of the handler cannot raise.
	(process_freeze_entity): Use Is_Record_Type.
	(process_type): Likewise.

From-SVN: r247484