Use is_empty_type instead of zero-sized type.

Use is_empty_type instead of zero-sized type.

Instead of only removing assignments of zero-sized types,
assignments of all empty types should be removed during gimplification.
This moves to use is_empty_type which will be used in other places too.

OK?  Bootstrapped and tested on aarch64-linux-gnu with no regressions.

Thanks,
Andrew Pinski

gcc/ChangeLog:

	* gimplify.c (zero_sized_field_decl): Delete
	(zero_sized_type): Delete
	(gimplify_init_ctor_eval): Use is_empty_type instead
	of zero_sized_field_decl.
	(gimplify_modify_expr): Use is_empty_type instead of
	zero_sized_type.