POSIX: fixes for gcc

GCC complains about strict prototypes.

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

src/platforms/posix/px4_layer/hrt_thread.c

@@ -71,6 +71,7 @@ sem_t _hrt_work_lock;
 /****************************************************************************
  * Private Functions
  ****************************************************************************/
+static void hrt_work_process(void);
 
 /****************************************************************************
  * Name: work_process

src/platforms/posix/px4_layer/hrt_work.h

@@ -46,8 +46,8 @@ void hrt_work_queue_init(void);
 int hrt_work_queue(struct work_s *work, worker_t worker, void *arg, uint32_t delay);
 void hrt_work_cancel(struct work_s *work);
 
-inline void hrt_work_lock();
-inline void hrt_work_unlock();
+inline void hrt_work_lock(void);
+inline void hrt_work_unlock(void);
 
 inline void hrt_work_lock()
 {