fixup: rt_current_thread as global

Author: polarvid

src/scheduler_up.c

@@ -48,7 +48,7 @@ rt_uint8_t rt_thread_ready_table[32];
 
 extern volatile rt_uint8_t rt_interrupt_nest;
 static rt_int16_t rt_scheduler_lock_nest;
-static struct rt_thread *rt_current_thread = RT_NULL;
+struct rt_thread *rt_current_thread = RT_NULL;
 rt_uint8_t rt_current_priority;
 
 #if defined(RT_USING_HOOK) && defined(RT_HOOK_USING_FUNC_PTR)