pthread: fixed pthread_cancel and pthread_exit crash in SMP mode

1. When pthread exit, set the default cancellability state to NONCANCELABLE state.
2. Make sure modify tcb->flags is atomic operations.

Signed-off-by: zhangyuan21 <zhangyuan21@xiaomi.com>

libs/libc/pthread/pthread_exit.c

@@ -58,9 +58,7 @@ void pthread_exit(FAR void *exit_value)
    * kicked off by actions taken during pthread_exit processing.
    */
 
-#ifdef CONFIG_CANCELLATION_POINTS
   task_setcancelstate(TASK_CANCEL_DISABLE, NULL);
-#endif
 
 #ifdef CONFIG_PTHREAD_CLEANUP
   pthread_cleanup_popall(tls_get_info());

sched/task/task_exithook.c

@@ -469,14 +469,14 @@ void nxtask_exithook(FAR struct tcb_s *tcb, int status)
     }
 #endif
 
-#ifdef CONFIG_SMP
-  leave_critical_section(flags);
-#endif
-
   /* This function can be re-entered in certain cases.  Set a flag
    * bit in the TCB to not that we have already completed this exit
    * processing.
    */
 
   tcb->flags |= TCB_FLAG_EXIT_PROCESSING;
+
+#ifdef CONFIG_SMP
+  leave_critical_section(flags);
+#endif
 }