macOS API for dealing with serial ports/ttys is identical to BSDs.

Signed-off-by: Mikhail Gusarov <dottedmag@dottedmag.net>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20200426210956.17324-1-dottedmag@dottedmag.net>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>