* ggc.h (struct alloc_zone): Move forward declaration up.
	(new_ggc_zone): New function prototype.
	(destroy_ggc_zone): Ditto.
	* ggc-simple.c (new_ggc_zone): New function, does nothing.
	(destroy_ggc_zone): Ditto.
	* ggc-page.c (new_ggc_zone): New function, does nothing.
	(destroy_ggc_zone): Ditto.
	* ggc-zone.c (struct page_entry): Fix comment.
	(ggc_alloc_typed): Use a switch statement instead of ifs.
	(new_ggc_zone): New function to set up a new GC zone.
	(destroy_ggc_zone): New function to remove a GC zone.
	init_ggc): Use new_ggc_zone to set up the default zones.
	(ggc_collect): Walk a list of zones, instead of just the
	default zones.  Report statistics using the zone name.

From-SVN: r74132