x86_64 ostest mqueue_test failing

The test seems to fail in two ways. With CONFIG_SCHED_CHILD_STATUS enabled
```
user_main: message queue test
mqueue_test: Starting receiver
mqueue_test: Set receiver priority to 128
receiver_thread: Starting
mqueue_test: Starting sender
mqueue_test: Set sender thread priority to 64
mqueue_test: Waiting for sender to complete
sender_thread: Starting
receiver_thread: mq_receive succeeded on msg 0
sender_thread: mq_send succeeded on msg 0
receiver_thread: mq_receive succeeded on msg 1
sender_thread: mq_send succeeded on msg 1
receiver_thread: mq_receive succeeded on msg 2
sender_thread: mq_send succeeded on msg 2
receiver_thread: mq_receive succeeded on msg 3
sender_thread: mq_send succeeded on msg 3
receiver_thread: mq_receive succeeded on msg 4
sender_thread: mq_send succeeded on msg 4
receiver_thread: mq_receive succeeded on msg 5
sender_thread: mq_send succeeded on msg 5
receiver_thread: mq_receive succeeded on msg 6
sender_thread: mq_send succeeded on msg 6
receiver_thread: mq_receive succeeded on msg 7
sender_thread: mq_send succeeded on msg 7
receiver_thread: mq_receive succeeded on msg 8
sender_thread: mq_send succeeded on msg 8
receiver_thread: mq_receive succeeded on msg 9
sender_thread: mq_send succeeded on msg 9
sender_thread: returning nerrors=0
mqueue_test: Killing receiver
up_sigdeliver: Deliver signal to 101982db0: 100914520
pthread_completejoin: ERROR: Could not find join info, pid=42
up_sigdeliver: Deliver signal to 101181190: 100914520
up_assert: Assertion failed at file:sched/sched_waitpid.c line: 554 task: ostest
up_sigdeliver: Deliver signal to 100d7ff90: 100914520
```

and when CONFIG_SCHED_CHILD_STATUS disabled in a different way
```
user_main: message queue test
mqueue_test: Starting receiver
mqueue_test: Set receiver priority to 128
receiver_thread: Starting
mqueue_test: Starting sender
mqueue_test: Set sender thread priority to 64
mqueue_test: Waiting for sender to complete
sender_thread: Starting
receiver_thread: mq_receive succeeded on msg 0
sender_thread: mq_send succeeded on msg 0
receiver_thread: mq_receive succeeded on msg 1
sender_thread: mq_send succeeded on msg 1
receiver_thread: mq_receive succeeded on msg 2
sender_thread: mq_send succeeded on msg 2
receiver_thread: mq_receive succeeded on msg 3
sender_thread: mq_send succeeded on msg 3
receiver_thread: mq_receive succeeded on msg 4
sender_thread: mq_send succeeded on msg 4
receiver_thread: mq_receive succeeded on msg 5
sender_thread: mq_send succeeded on msg 5
receiver_thread: mq_receive succeeded on msg 6
sender_thread: mq_send succeeded on msg 6
receiver_thread: mq_receive succeeded on msg 7
sender_thread: mq_send succeeded on msg 7
receiver_thread: mq_receive succeeded on msg 8
sender_thread: mq_send succeeded on msg 8
receiver_thread: mq_receive succeeded on msg 9
sender_thread: mq_send succeeded on msg 9
sender_thread: returning nerrors=0
mqueue_test: Killing receiver
up_sigdeliver: Deliver signal to 102582b30: 1009130b1
mqueue_test: Canceling receiver
mqueue_test: receiver has already terminated
mqueue_test: ERROR send mqd_t left open
```