Make all the serialization code build for the Teensy too

Change-Id: Ib3442220581553d78bb30e42818203959d987d85
diff --git a/y2019/jevois/uart.h b/y2019/jevois/uart.h
index 87dcc97..2a4acec 100644
--- a/y2019/jevois/uart.h
+++ b/y2019/jevois/uart.h
@@ -2,6 +2,7 @@
 #define Y2019_JEVOIS_UART_H_
 
 #include "aos/containers/sized_array.h"
+#include "third_party/GSL/include/gsl/gsl"
 #include "third_party/optional/tl/optional.hpp"
 #include "y2019/jevois/cobs.h"
 #include "y2019/jevois/structures.h"