AP_HAL: don't include Semaphore headers while building C source

libraries/AP_HAL/board/chibios.h

@@ -59,12 +59,14 @@
 #define HAL_WITH_EKF_DOUBLE HAL_HAVE_HARDWARE_DOUBLE
 #endif
 
+#ifdef __cplusplus
 // allow for static semaphores
 #include <AP_HAL_ChibiOS/Semaphores.h>
 #define HAL_Semaphore ChibiOS::Semaphore
 
 #include <AP_HAL/EventHandle.h>
 #define HAL_EventHandle AP_HAL::EventHandle
+#endif
 
 /* string names for well known SPI devices */
 #define HAL_BARO_MS5611_NAME "ms5611"

libraries/AP_HAL/board/esp32.h

@@ -23,9 +23,11 @@
 #define O_CLOEXEC 0
 #define HAL_STORAGE_SIZE (16384)
 
+#ifdef __cplusplus
 // allow for static semaphores
 #include <AP_HAL_ESP32/Semaphores.h>
 #define HAL_Semaphore ESP32::Semaphore
+#endif
 
 #define HAL_NUM_CAN_IFACES 0
 #define HAL_MEM_CLASS HAL_MEM_CLASS_192

libraries/AP_HAL/board/linux.h

@@ -380,10 +380,13 @@
     #define HAL_LINUX_I2C_EXTERNAL_BUS_MASK 0xFFFF
 #endif
 
+// only include if compiling C++ code
+#ifdef __cplusplus
 #include <AP_HAL_Linux/Semaphores.h>
 #define HAL_Semaphore Linux::Semaphore
 #include <AP_HAL/EventHandle.h>
 #define HAL_EventHandle AP_HAL::EventHandle
+#endif
 
 #ifndef HAL_HAVE_HARDWARE_DOUBLE
 #define HAL_HAVE_HARDWARE_DOUBLE 1

libraries/AP_HAL/board/sitl.h

@@ -50,12 +50,15 @@
 #define HAL_HAVE_SERVO_VOLTAGE 1
 #define HAL_HAVE_SAFETY_SWITCH 0
 
+// only include if compiling C++ code
+#ifdef __cplusplus
 // allow for static semaphores
 #include <AP_HAL_SITL/Semaphores.h>
 #define HAL_Semaphore HALSITL::Semaphore
 
 #include <AP_HAL/EventHandle.h>
 #define HAL_EventHandle AP_HAL::EventHandle
+#endif
 
 #ifndef HAL_NUM_CAN_IFACES
 #define HAL_NUM_CAN_IFACES 0