event-loop.c: Use correct OS abstraction function for dupfd()

Signed-off-by: Philip Withnall <philip at tecnocode.co.uk>
Signed-off-by: Karsten Otto <ottoka at posteo.de>
Reviewed-by: David Fort <contact at hardening-consulting.com>
Reviewed-by: Marek Chalupa <mchqwerty@gmail.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>