When suspend current thread and then enable interrupt, it's possible resume "the current thread" immediately and insert to ready queue. The rt_schedule_insert_thread should change  the status of "current thread" to RUNNING statue.

sync smp skeleton

2 RTM_EXPORT(rt_cpus_lock_status_restore)
3 sync ARCH_CPU_STACK_GROWS_UPWARD in _rt_scheduler_stack_check()

Update license for RT-Thread kernel.

1. Add signal implementation;
2. Change the 'rt_uint8_t' of cmd to 'int';