Minor code refactoring of dumping routines related to 'long' links

Minor code refactoring of dumping routines related to 'long' links

* finalize.c (struct disappearing_link): Remove STATIC.
* finalize.c (GC_dl_hashtbl, GC_ll_hashtbl): Define separately from
dl_hashtbl_s definition.
* finalize.c (GC_grow_table): Reformat comment.
* finalize.c (GC_dump_finalization_links): Pass 'dl_hashtbl' argument
as pointer to constant struct.
* finalize.c (GC_dump_finalization_links, GC_dump_finalization):
Adjust printed message.
* finalize.c (GC_old_ll_entries): Do not define if
GC_LONG_REFS_NOT_NEEDED.
* finalize.c (IF_LONG_REFS_PRESENT_ELSE): New macro (only if not
SMALL_CONFIG).
* finalize.c (GC_print_finalization_stats): Use
IF_LONG_REFS_PRESENT_ELSE (instead of testing GC_LONG_REFS_NOT_NEEDED);
make printed messages more compact.