Fix RTOS function prototypes by adding extern "C"

Wrap the file mbed_rtos_storage.h in extern "C". This allows the
functions inside rtx_lib.h to have correct definitions when included
in a C++ file.

This is required for the RTX5 error trapping.

rtos/mbed_rtos_storage.h

@@ -22,6 +22,10 @@
 #ifndef MBED_RTOS_STORAGE_H
 #define MBED_RTOS_STORAGE_H
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 /** \addtogroup rtos */
 /** @{*/
 
@@ -47,6 +51,10 @@ typedef os_event_flags_t mbed_rtos_storage_event_flags_t;
 typedef os_message_t mbed_rtos_storage_message_t;
 typedef os_timer_t mbed_rtos_storage_timer_t;
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif
 
 /** @}*/