AP_GPS: add override keyword where required

libraries/AP_GPS/AP_GPS_ERB.h

@@ -30,11 +30,11 @@ public:
     AP_GPS_ERB(AP_GPS &_gps, AP_GPS::GPS_State &_state, AP_HAL::UARTDriver *_port);
 
     // Methods
-    bool read();
+    bool read() override;
 
-    AP_GPS::GPS_Status highest_supported_status(void) { return AP_GPS::GPS_OK_FIX_3D_RTK_FIXED; }
+    AP_GPS::GPS_Status highest_supported_status(void) override { return AP_GPS::GPS_OK_FIX_3D_RTK_FIXED; }
 
-    bool supports_mavlink_gps_rtk_message() { return true; }
+    bool supports_mavlink_gps_rtk_message() override { return true; }
 
     static bool _detect(struct ERB_detect_state &state, uint8_t data);
 

libraries/AP_GPS/AP_GPS_GSOF.h

@@ -27,12 +27,12 @@ class AP_GPS_GSOF : public AP_GPS_Backend
 public:
     AP_GPS_GSOF(AP_GPS &_gps, AP_GPS::GPS_State &_state, AP_HAL::UARTDriver *_port);
 
-    AP_GPS::GPS_Status highest_supported_status(void) {
+    AP_GPS::GPS_Status highest_supported_status(void) override {
         return AP_GPS::GPS_OK_FIX_3D_RTK_FIXED;
     }
 
     // Methods
-    bool read();
+    bool read() override;
 
     const char *name() const override { return "GSOF"; }
 

libraries/AP_GPS/AP_GPS_MAV.h

@@ -29,11 +29,11 @@ class AP_GPS_MAV : public AP_GPS_Backend {
 public:
     AP_GPS_MAV(AP_GPS &_gps, AP_GPS::GPS_State &_state, AP_HAL::UARTDriver *_port);
 
-    bool read();
+    bool read() override;
 
     static bool _detect(struct MAV_detect_state &state, uint8_t data);
 
-    void handle_msg(const mavlink_message_t *msg);
+    void handle_msg(const mavlink_message_t *msg) override;
 
     const char *name() const override { return "MAV"; }
 

libraries/AP_GPS/AP_GPS_MTK.h

@@ -31,7 +31,7 @@ class AP_GPS_MTK : public AP_GPS_Backend {
 public:
     AP_GPS_MTK(AP_GPS &_gps, AP_GPS::GPS_State &_state, AP_HAL::UARTDriver *_port);
 
-    bool read(void);
+    bool read(void) override;
 
     static bool _detect(struct MTK_detect_state &state, uint8_t data);
     static void send_init_blob(uint8_t instance, AP_GPS &gps);

libraries/AP_GPS/AP_GPS_MTK19.h

@@ -32,7 +32,7 @@ class AP_GPS_MTK19 : public AP_GPS_Backend {
 public:
     AP_GPS_MTK19(AP_GPS &_gps, AP_GPS::GPS_State &_state, AP_HAL::UARTDriver *_port);
 
-    bool        read(void);
+    bool        read(void) override;
 
     static bool _detect(struct MTK19_detect_state &state, uint8_t data);
 

libraries/AP_GPS/AP_GPS_NMEA.h

@@ -58,7 +58,7 @@ public:
     /// Checks the serial receive buffer for characters,
     /// attempts to parse NMEA data and updates internal state
     /// accordingly.
-    bool        read();
+    bool        read() override;
 
 	static bool _detect(struct NMEA_detect_state &state, uint8_t data);
 

libraries/AP_GPS/AP_GPS_NOVA.h

@@ -27,10 +27,10 @@ class AP_GPS_NOVA : public AP_GPS_Backend
 public:
     AP_GPS_NOVA(AP_GPS &_gps, AP_GPS::GPS_State &_state, AP_HAL::UARTDriver *_port);
 
-    AP_GPS::GPS_Status highest_supported_status(void) { return AP_GPS::GPS_OK_FIX_3D_RTK_FIXED; }
+    AP_GPS::GPS_Status highest_supported_status(void) override { return AP_GPS::GPS_OK_FIX_3D_RTK_FIXED; }
 
     // Methods
-    bool read();
+    bool read() override;
 
     void inject_data(const uint8_t *data, uint16_t len) override;
 

libraries/AP_GPS/AP_GPS_SBF.h

@@ -32,10 +32,10 @@ class AP_GPS_SBF : public AP_GPS_Backend
 public:
     AP_GPS_SBF(AP_GPS &_gps, AP_GPS::GPS_State &_state, AP_HAL::UARTDriver *_port);
 
-    AP_GPS::GPS_Status highest_supported_status(void) { return AP_GPS::GPS_OK_FIX_3D_RTK_FIXED; }
+    AP_GPS::GPS_Status highest_supported_status(void) override { return AP_GPS::GPS_OK_FIX_3D_RTK_FIXED; }
 
     // Methods
-    bool read();
+    bool read() override;
 
     const char *name() const override { return "SBF"; }
 

libraries/AP_GPS/AP_GPS_SBP.h

@@ -29,12 +29,12 @@ class AP_GPS_SBP : public AP_GPS_Backend
 public:
     AP_GPS_SBP(AP_GPS &_gps, AP_GPS::GPS_State &_state, AP_HAL::UARTDriver *_port);
 
-    AP_GPS::GPS_Status highest_supported_status(void) { return AP_GPS::GPS_OK_FIX_3D_RTK_FIXED; }
+    AP_GPS::GPS_Status highest_supported_status(void) override { return AP_GPS::GPS_OK_FIX_3D_RTK_FIXED; }
 
-    bool supports_mavlink_gps_rtk_message() { return true; }
+    bool supports_mavlink_gps_rtk_message() override { return true; }
 
     // Methods
-    bool read();
+    bool read() override;
 
     void inject_data(const uint8_t *data, uint16_t len) override;
 

libraries/AP_GPS/AP_GPS_SIRF.h

@@ -31,7 +31,7 @@ class AP_GPS_SIRF : public AP_GPS_Backend {
 public:
 	AP_GPS_SIRF(AP_GPS &_gps, AP_GPS::GPS_State &_state, AP_HAL::UARTDriver *_port);
 
-    bool read();
+    bool read() override;
 
 	static bool _detect(struct SIRF_detect_state &state, uint8_t data);
 

libraries/AP_GPS/AP_GPS_UBLOX.h

@@ -95,13 +95,13 @@ public:
 	AP_GPS_UBLOX(AP_GPS &_gps, AP_GPS::GPS_State &_state, AP_HAL::UARTDriver *_port);
 
     // Methods
-    bool read();
+    bool read() override;
 
-    AP_GPS::GPS_Status highest_supported_status(void) { return AP_GPS::GPS_OK_FIX_3D_RTK_FIXED; }
+    AP_GPS::GPS_Status highest_supported_status(void) override { return AP_GPS::GPS_OK_FIX_3D_RTK_FIXED; }
 
     static bool _detect(struct UBLOX_detect_state &state, uint8_t data);
 
-    bool is_configured(void) {
+    bool is_configured(void) override {
 #if CONFIG_HAL_BOARD != HAL_BOARD_SITL
         if (!gps._auto_config) {
             return true;