Rename mjit_gc_finish_hook to mjit_gc_exit_hook
because @ko1 (Koichi Sasada) said "gc_finish" is confusing like a finish of entire GC process
Rename mjit_gc_finish_hook to mjit_gc_exit_hook
because @ko1 (Koichi Sasada) said "gc_finish" is confusing like a finish of entire GC
process