Include <stdio> if iocp logging is enabled

Change-Id: I4fb38ab38fc43320822fafb3a83cd32b3e78de00
Reviewed-on: http://review.couchbase.org/27807
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>