Port pool-allocator memory stats to a new infrastructure.

	* alloc-pool.c (allocate_pool_descriptor): Remove.
	(struct pool_output_info): Likewise.
	(print_alloc_pool_statistics): Likewise.
	(dump_alloc_pool_statistics): Likewise.
	* alloc-pool.h (struct pool_usage): New struct.
	(pool_allocator::initialize): Change usage of memory statistics
	to a new interface.
	(pool_allocator::release): Likewise.
	(pool_allocator::allocate): Likewise.
	(pool_allocator::remove): Likewise.
	* mem-stats-traits.h (enum mem_alloc_origin): Add new enum value
	for a pool allocator.
	* mem-stats.h (struct mem_location): Add new ctor.
	(struct mem_usage): Add counter for number of
	instances.
	(mem_alloc_description::register_descriptor): New overload of
	* mem-stats.h (mem_location::to_string): New function.
	* bitmap.h (struct bitmap_usage): Use this new function.
	* ggc-common.c (struct ggc_usage): Likewise.
	the function.

From-SVN: r224070