GCS_MAVLink: allow for mavlink bindings only in GCS_MAVLink

this is used by SITL periph to allow for mavlink based simulators

libraries/GCS_MAVLink/GCS_MAVLink.cpp

@@ -22,7 +22,7 @@ This provides some support code and variables for MAVLink enabled sketches
 
 #include "GCS_config.h"
 
-#if HAL_GCS_ENABLED
+#if HAL_MAVLINK_BINDINGS_ENABLED
 
 #include "GCS.h"
 #include "GCS_MAVLink.h"
@@ -41,6 +41,10 @@ extern const AP_HAL::HAL& hal;
 #pragma GCC diagnostic pop
 #endif
 
+#endif // HAL_MAVLINK_BINDINGS_ENABLED
+
+#if HAL_GCS_ENABLED
+
 AP_HAL::UARTDriver	*mavlink_comm_port[MAVLINK_COMM_NUM_BUFFERS];
 bool gcs_alternative_active[MAVLINK_COMM_NUM_BUFFERS];
 
@@ -180,3 +184,13 @@ HAL_Semaphore &comm_chan_lock(mavlink_channel_t chan)
 }
 
 #endif  // HAL_GCS_ENABLED
+
+#if HAL_MAVLINK_BINDINGS_ENABLED && !HAL_GCS_ENABLED
+/*
+  this allows for SITL bindings for constructing mavlink messages
+ */
+mavlink_status_t* mavlink_get_channel_status(uint8_t chan)
+{
+    return nullptr;
+}
+#endif

libraries/GCS_MAVLink/GCS_config.h

@@ -7,6 +7,10 @@
 #define HAL_GCS_ENABLED 1
 #endif
 
+#ifndef HAL_MAVLINK_BINDINGS_ENABLED
+#define HAL_MAVLINK_BINDINGS_ENABLED HAL_GCS_ENABLED
+#endif
+
 // BATTERY2 is slated to be removed:
 #ifndef AP_MAVLINK_BATTERY2_ENABLED
 #define AP_MAVLINK_BATTERY2_ENABLED 1