Guard the lockstat:::thread-spin probe with KDTRACE_HOOKS.

X-MFC-With:	r300103

sys/kern/kern_mutex.c

@@ -714,8 +714,10 @@ thread_lock_flags_(struct thread *td, int opts, const char *file, int line)
 	LOCK_LOG_LOCK("LOCK", &m->lock_object, opts, m->mtx_recurse, file,
 	    line);
 	WITNESS_LOCK(&m->lock_object, opts | LOP_EXCLUSIVE, file, line);
+#ifdef KDTRACE_HOOKS
 	if (spin_time != 0)
 		LOCKSTAT_RECORD1(thread__spin, m, spin_time);
+#endif
 }
 
 struct mtx *