fix FFSYNC by changing it to O_SYNC

O_FSYNC was never defined and is legacy/wrong, nothing seems to use it.
diff --git a/include/fcntl.h b/include/fcntl.h
index e683e4d..0e165ca 100644
--- a/include/fcntl.h
+++ b/include/fcntl.h
@@ -99,7 +99,7 @@
 #define AT_EMPTY_PATH 0x1000
 
 #define FAPPEND O_APPEND
-#define FFSYNC O_FSYNC
+#define FFSYNC O_SYNC
 #define FASYNC O_ASYNC
 #define FNONBLOCK O_NONBLOCK
 #define FNDELAY O_NDELAY