* ggc-zone.c (struct alloc_zone): Don't pre-declare, it already

	* ggc-zone.c (struct alloc_zone): Don't pre-declare, it already
	comes in with ggc.h.  Add a new bool field `dead'.
	(destroy_ggc_zone): Don't destroy a zone at once.  Instead, only
	set the `dead' flag for the dead zone.  Wrap a sanity check in
	ENABLE_CHECKING.
	(ggc_collect_1): Always mark and sweep if a zone has the `dead'
	flag set.
	(ggc_collect): Free dead zones after collecting.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@74592 138bc75d-0d04-0410-961f-82ee72b054a4