Enable C++ support for socket debug transport

examples/debug-trans-socket/duk_trans_socket.h

@@ -3,6 +3,10 @@
 
 #include "duktape.h"
 
+#if defined(__cplusplus)
+extern "C" {
+#endif
+
 void duk_trans_socket_init(void);
 void duk_trans_socket_finish(void);
 void duk_trans_socket_waitconn(void);
@@ -12,4 +16,8 @@ duk_size_t duk_trans_socket_peek_cb(void *udata);
 void duk_trans_socket_read_flush_cb(void *udata);
 void duk_trans_socket_write_flush_cb(void *udata);
 
+#if defined(__cplusplus)
+}
+#endif  /* end 'extern "C"' wrapper */
+
 #endif  /* DUK_TRANS_SOCKET_H_INCLUDED */