HP-UX: add fdatasync()

Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
diff --git a/os/os-hpux.h b/os/os-hpux.h
index 0e8152b..d7397bf 100644
--- a/os/os-hpux.h
+++ b/os/os-hpux.h
@@ -25,6 +25,7 @@
 #define FIO_HAVE_CHARDEV_SIZE
 #define FIO_HAVE_FALLOCATE
 #define FIO_HAVE_POSIXAIO_FSYNC
+#define FIO_HAVE_FDATASYNC
 
 #define OS_MAP_ANON		MAP_ANONYMOUS
 #define OS_MSG_DONTWAIT		0