* gigi.h (mark_visited): Declare.
	* decl.c (gnat_to_gnu_entity): Use mark_visited instead of marking
	only the topmost node of expressions.
	(elaborate_expression_1): Look deeper for read-only variable.
	* trans.c (add_decl_expr): Use mark_visited instead of marking by hand.
	(mark_visited): Move logic to mark_visited_r.  Invoke walk_tree.
	(mark_visited_r): New function.

From-SVN: r135819