Rewrite how instances of passes are cloned

Rewrite how instances of passes are cloned

gcc/

	Rewrite how instances of passes are cloned to remove assumptions
	about their sizes (thus allowing pass subclasses to have
	additional data fields, albeit non-GC-managed ones at this point).

	* passes.c (make_pass_instance): Now that passes have clone
	methods, rewrite this function to eliminate XNEW and memcpy
	calls that used hardcoded sizes.  Since this function no longer
	creates pass instances, rename it to...
	(add_pass_instance): ...this.  Document the old way that passes
	were numbered and flagged, and rework this function to continue
	using it.
	(next_pass_1): Add an initial_pass argument for use by
	add_pass_instance.
	(position_pass): When adding multiple instances of a pass, use
	the pass's clone method, rather than relying on the XNEW/memcpy
	within the former make_pass_instance (now add_pass_instance).
	(pass_manager::pass_manager): When invoking next_pass_1, also
	supply the initial instance of the current pass within the
	pass manager.

From-SVN: r201511