From: Manfred Spraul <manfred@colorfullife.com>

Add -ENOSYS stubs for the posix message queue syscalls.  The API is a direct
mapping of the api from the unix spec, with two exceptions:

- mq_close() doesn't exist.  Message queue file descriptors can be closed
  with close().

- mq_notify(SIGEV_THREAD) cannot be implemented in the kernel.  The kernel
  returns a pollable file descriptor .  User space must poll (or read) this
  descriptor and call the notifier function if the file descriptor is
  signaled.