[O_DIRECT] Use posix_memalign to allocate 4KiB-aligned pages for writing to an O_DIRECT fd.
[O_DIRECT] Use posix_memalign to allocate 4KiB-aligned pages for writing to an O_DIRECT fd.

Signed-off-by: David Scott <63c9eb0ea83039690fefa11afe17873ba8278a56@eu.citrix.com>

johnelse/forkexecd,xapi-project/message-switch,djs55/forkexecd,xapi-project/message-switch,xapi-project/message-switch