QuRT: Changes to enable qurt target to build

QuRT doesn't support unlink and does not provide getpid().
The DSPAL layer provides access to usleep so an implementation is
no longer needed.

Signed-off-by: Mark Charlebois <charlebm@gmail.com>

src/modules/mavlink/mavlink_main.h

@@ -395,12 +395,14 @@ private:
 	float			_rate_txerr;
 	float			_rate_rx;
 
+#ifdef __PX4_POSIX
 	int _socket_fd;
 	struct sockaddr_in _myaddr;
 	struct sockaddr_in _src_addr;
 
 	Protocol	_protocol;
 	unsigned short _udp_port;
+#endif
 
 	struct telemetry_status_s	_rstatus;			///< receive status
 

src/modules/uORB/uORBDevices_posix.cpp

@@ -91,7 +91,7 @@ uORB::DeviceNode::open(device::file_t *filp)
     lock();
 
     if (_publisher == 0) {
-      _publisher = getpid();
+      _publisher = px4_getpid();
       ret = PX4_OK;
 
     } else {
@@ -153,7 +153,7 @@ uORB::DeviceNode::close(device::file_t *filp)
 {
   //warnx("uORB::DeviceNode::close fd = %d", filp->fd);
   /* is this the publisher closing? */
-  if (getpid() == _publisher) {
+  if (px4_getpid() == _publisher) {
     _publisher = 0;
 
   } else {