py/stream: Stream module works with errno's, so should include mperrno.h.
diff --git a/py/stream.h b/py/stream.h
index bd3fa0b..28e0d2d 100644
--- a/py/stream.h
+++ b/py/stream.h
@@ -27,6 +27,7 @@
 #define __MICROPY_INCLUDED_PY_STREAM_H__
 
 #include "py/obj.h"
+#include "py/mperrno.h"
 
 #define MP_STREAM_ERROR ((mp_uint_t)-1)