HAL_Linux: resync for 4.0 update

libraries/AP_HAL_Linux/Scheduler.cpp

@@ -237,9 +237,7 @@ void Scheduler::_timer_task()
 
 void Scheduler::_run_io(void)
 {
-    if (!_io_semaphore.take(HAL_SEMAPHORE_BLOCK_FOREVER)) {
+    _io_semaphore.take_blocking();
-        return;
-    }
 
     // now call the IO based drivers
     for (int i = 0; i < _num_io_procs; i++) {

libraries/AP_HAL_Linux/Semaphores.cpp

@@ -8,12 +8,6 @@ using namespace Linux;
 
 // construct a semaphore
 Semaphore::Semaphore()
-{
-    pthread_mutex_init(&_lock, nullptr);
-}
-
-// construct a recursive semaphore (allows a thread to take it more than once)
-Semaphore_Recursive::Semaphore_Recursive()
 {
     pthread_mutexattr_t attr;
     pthread_mutexattr_init(&attr);

libraries/AP_HAL_Linux/Semaphores.h

@@ -18,9 +18,4 @@ protected:
     pthread_mutex_t _lock;
 };
 
-class Semaphore_Recursive : public Semaphore {
-public:
-    Semaphore_Recursive();
-};
-    
 }

libraries/AP_HAL_Linux/system.cpp

@@ -30,8 +30,12 @@ void panic(const char *errormsg, ...)
     va_end(ap);
     UNUSED_RESULT(write(1, "\n", 1));
 
+    if (hal.rcin != nullptr) {
         hal.rcin->teardown();
+    }
+    if (hal.scheduler != nullptr) {
         hal.scheduler->delay_microseconds(10000);
+    }
     exit(1);
 }