[Libvir] 8/22 no O_SYNC

There is no O_SYNC in the Win32 API. This general patch disables it as suggested by Jim Meyering yesterday. Rich. -- Emerging Technologies, Red Hat - http://et.redhat.com/~rjones/ Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SL4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 03798903