Fix -Werror=implicit-fallthrough errors on GCC7

src/drivers/gps/gps.cpp

@@ -684,8 +684,8 @@ GPS::task_main()
 			switch (_mode) {
 			case GPS_DRIVER_MODE_NONE:
 				_mode = GPS_DRIVER_MODE_UBX;
+				/* FALLTHROUGH */
 
-			//no break
 			case GPS_DRIVER_MODE_UBX:
 				_helper = new GPSDriverUBX(_interface, &GPS::callback, this, &_report_gps_pos, _p_report_sat_info);
 				break;

src/drivers/pwm_out_sim/pwm_out_sim.cpp

@@ -718,8 +718,8 @@ PWMSim::pwm_ioctl(device::file_t *filp, int cmd, unsigned long arg)
 			ret = -EINVAL;
 			break;
 		}
+		/* FALLTHROUGH */
 
-	/* FALLTHROUGH */
 	case PWM_SERVO_SET(0):
 	case PWM_SERVO_SET(1):
 		if (arg < 2100) {
@@ -740,6 +740,7 @@ PWMSim::pwm_ioctl(device::file_t *filp, int cmd, unsigned long arg)
 			ret = -EINVAL;
 			break;
 		}
+		/* FALLTHROUGH */
 
 	case PWM_SERVO_GET(3):
 	case PWM_SERVO_GET(2):
@@ -747,8 +748,8 @@ PWMSim::pwm_ioctl(device::file_t *filp, int cmd, unsigned long arg)
 			ret = -EINVAL;
 			break;
 		}
+		/* FALLTHROUGH */
 		
-	/* FALLTHROUGH */
 	case PWM_SERVO_GET(1):
 	case PWM_SERVO_GET(0): {
 			*(servo_position_t *)arg = 1500;

src/drivers/vmount/input_mavlink.cpp

@@ -231,8 +231,8 @@ int InputMavlinkCmdMount::update_impl(unsigned int timeout_ms, ControlData **con
 				switch ((int)vehicle_command.param7) {
 				case vehicle_command_s::VEHICLE_MOUNT_MODE_RETRACT:
 					_control_data.gimbal_shutter_retract = true;
+					/* FALLTHROUGH */
 
-				//no break
 				case vehicle_command_s::VEHICLE_MOUNT_MODE_NEUTRAL:
 					_control_data.type = ControlData::Type::Neutral;
 
@@ -306,4 +306,3 @@ void InputMavlinkCmdMount::print_status()
 
 
 } /* namespace vmount */
-

src/modules/navigator/follow_target.cpp

@@ -336,6 +336,7 @@ void FollowTarget::on_active()
 
 			_follow_target_state = WAIT_FOR_TARGET_POSITION;
 		}
+		/* FALLTHROUGH */
 
 	case WAIT_FOR_TARGET_POSITION: {