GCS_MAVLINK: provide a GCS singleton for examples and tools to use

libraries/GCS_MAVLink/GCS_Dummy.h

@@ -0,0 +1,31 @@
+#include "GCS.h"
+
+/*
+ *  GCS backend used for many examples and tools
+ */
+class GCS_MAVLINK_Dummy : public GCS_MAVLINK
+{
+    void data_stream_send(void) override {}
+    uint32_t telem_delay() const override { return 0; }
+    void handleMessage(mavlink_message_t * msg) override {}
+    bool try_send_message(enum ap_message id) { return true; }
+    bool handle_guided_request(AP_Mission::Mission_Command &cmd) override { return true; }
+    void handle_change_alt_request(AP_Mission::Mission_Command &cmd) override {}
+};
+
+/*
+ * a GCS singleton used for many example sketches and tools
+ */
+
+extern const AP_HAL::HAL& hal;
+
+class GCS_Dummy : public GCS
+{
+    GCS_MAVLINK_Dummy dummy_backend;
+    uint8_t num_gcs() const override { return 1; }
+    GCS_MAVLINK &chan(const uint8_t ofs) override { return dummy_backend; }
+    bool cli_enabled() const override { return false; }
+    AP_HAL::BetterStream*  cliSerial() { return nullptr; }
+
+    void send_statustext(MAV_SEVERITY severity, uint8_t dest_bitmask, const char *text) { hal.console->printf("TOGCS: %s\n", text); }
+};