AP_Mission: fix example by instantiating a GCS object

libraries/AP_Mission/examples/AP_Mission_test/AP_Mission_test.cpp

@@ -11,9 +11,14 @@
 #include <AP_Compass/AP_Compass.h>
 #include <AP_AHRS/AP_AHRS.h>
 #include <AP_AHRS/AP_AHRS_DCM.h>
+#include <GCS_MAVLink/GCS_Dummy.h>
 
 const AP_HAL::HAL& hal = AP_HAL::get_HAL();
 
+const struct AP_Param::GroupInfo        GCS_MAVLINK::var_info[] = {
+    AP_GROUPEND
+};
+
 class MissionTest {
 public:
     void setup();
@@ -25,6 +30,7 @@ private:
     AP_GPS  gps;
     Compass compass;
     AP_AHRS_DCM ahrs{};
+    GCS_Dummy _gcs;
 
     // global constants that control how many verify calls must be made for a command before it completes
     uint8_t verify_nav_cmd_iterations_to_complete = 3;