7024970: 2/3 assert(ServiceThread::is_service_thread(Thread::current())) failed: Service thread must post enqueue Summary: Change nmethod_lock() to also prevent zombification of the nmethod. CompiledMethodUnload events also need to lock the nmethod. Clean ups in nmethod::make_not_entrant_or_zombie() Reviewed-by: dholmes, kamg, never, dsamersoff, ysr, coleenp, acorn