* gold.cc (gold_exit): Call plugin cleanup handlers on exit.

	* gold.cc (gold_exit): Call plugin cleanup handlers on exit.
	* plugin.cc (Plugin_manager::finish): Rename as
	layout_deferred_objects.  Move cleanup to separate function.
	(Plugin_manager::cleanup): New function.
	(Plugin_finish::run): Call layout_deferred_objects and cleanup
	separately.
	* plugin.h (Plugin_manager::finish): Rename as
	layout_deferred_objects.
	(Plugin_manager::cleanup): New function.
	(Plugin_manager::cleanup_done): New field.