TEENSY: add missing file

Author: Chris Warren-Smith

src/platform/teensy/src/serial.h

@@ -0,0 +1,12 @@
+// This file is part of SmallBASIC
+//
+// Copyright(C) 2001-2025 Chris Warren-Smith.
+// Copyright(C) 2000 Nicholas Christopoulos
+//
+// This program is distributed under the terms of the GPL v2.0 or later
+// Download the GNU Public License (GPL) from www.gnu.org
+//
+
+#pragma once
+
+void serial_init();