libc: Call pthread_exit in user-space by up_pthread_exit

Drop to user-space in kernel/protected build with up_pthread_exit,
now all pthread_cleanup functions executed in user mode.

* A new syscall SYS_pthread_exit added
* A new tcb flag TCB_FLAG_CANCEL_DOING added
* up_pthread_exit implemented for riscv/arm arch

Signed-off-by: Huang Qi <huangqi3@xiaomi.com>

sched/task/task_setcancelstate.c

@@ -112,7 +112,15 @@ int task_setcancelstate(int state, FAR int *oldstate)
               if ((tcb->flags & TCB_FLAG_TTYPE_MASK) ==
                   TCB_FLAG_TTYPE_PTHREAD)
                 {
+#if !defined(CONFIG_BUILD_FLAT) && defined(__KERNEL__)
+                  tcb->flags &= ~TCB_FLAG_CANCEL_PENDING;
+                  tcb->flags |= TCB_FLAG_CANCEL_DOING;
+
+                  up_pthread_exit(((FAR struct pthread_tcb_s *)tcb)->exit,
+                                  PTHREAD_CANCELED);
+#else
                   pthread_exit(PTHREAD_CANCELED);
+#endif
                 }
               else
 #endif