* Simplify EINTR/ECANCEL error handling
1. Add semaphore uninterruptible wait function
2 .Replace semaphore wait loop with a single uninterruptible wait
3. Replace all sem_xxx to nxsem_xxx
* Unify the void cast usage
1. Remove void cast for function because many place ignore the returned value witout cast
2. Replace void cast for variable with UNUSED macro
Change all calls to mq_send() and mq_timedsend() in the OS to calls to nxmq_send() and nxmq_timedsend(), making appropriate changes for differences in return values.
sched/mqueue: Add internal function nxmq_send() and nxmq_timedsend() that are equivalent to mq_send() and mq_timedsend() except that they do not create cancellation points and do to not modify the errno variable.
sched/mqueue: Rename all private static functions for use the nxmq_ vs. mq_ naming.
sched/mqueue: Rename all OS internal functions declared in sched/mqueue/mqueue.h to begin with nxmq_ vs. mq_. The mq_ prefix is reserved for standard application interfaces.
