Substitute O_DSYNC with O_SYNC or O_FSYNC when needed.

Signed-off-by: John Arbuckle <programmingkidx@gmail.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

block/raw-posix.c

@@ -81,7 +81,11 @@
 
 /* OS X does not have O_DSYNC */
 #ifndef O_DSYNC
+#ifdef O_SYNC
 #define O_DSYNC O_SYNC
+#elif defined(O_FSYNC)
+#define O_DSYNC O_FSYNC
+#endif
 #endif
 
 /* Approximate O_DIRECT with O_DSYNC if O_DIRECT isn't available */