add C++ include guards to header files which are missing them

Fixes https://github.com/espressif/esp-idf/issues/628

components/esp32/include/esp_ipc.h

@@ -17,6 +17,10 @@
 
 #include <esp_err.h>
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 typedef void (*esp_ipc_func_t)(void* arg);
 
 /**
@@ -84,5 +88,8 @@ esp_err_t esp_ipc_call(uint32_t cpu_id, esp_ipc_func_t func, void* arg);
 esp_err_t esp_ipc_call_blocking(uint32_t cpu_id, esp_ipc_func_t func, void* arg);
 
 
+#ifdef __cplusplus
+}
+#endif
 
 #endif /* __ESP_IPC_H__ */