This implements finalizers by keeping a list of registered finalizers
and after every mark but before sweeping check to see if any of them are
for unmarked blocks.

gcc/ChangeLog:

	* ggc-common.c (ggc_internal_cleared_alloc): Adjust.
	* ggc-none.c (ggc_internal_alloc): Assert if a finalizer is passed.
	(ggc_internal_cleared_alloc): Likewise.
	* ggc-page.c (finalizer): New class.
(vec_finalizer): Likewise.
	(globals::finalizers): New member.
(globals::vec_finalizers): Likewise.
	(ggc_internal_alloc): Record the finalizer if any for the block being
	allocated.
	(ggc_handle_finalizers): New function.
	(ggc_collect): Call ggc_handle_finalizers.
	* ggc.h (ggc_internal_alloc): Add arguments to allow installing a
	finalizer.
	(ggc_internal_cleared_alloc): Likewise.
	(finalize): New function.
	(need_finalization_p): Likewise.
	(ggc_alloc): Install the type's destructor as the finalizer if it
	might do something.
	(ggc_cleared_alloc): Likewise.
	(ggc_vec_alloc): Likewise.
	(ggc_cleared_vec_alloc): Likewise.

From-SVN: r210568