Although the MY_SYNC_DIR flag supported in my_create(), my_delete(),
   my_rename() and my_symlink(), this feature is not used in the
   mysql code now. So technically we can declare the MY_SYNC_DIR as 0,
   but I decided to assign a new value for it as it's probably safer and
   worths nothing.

per-file comments:
  include/my_sys.h
Bug#47126      equal flag values causing unexpected behaviour
     assign unique value for the MY_SYNC_DIR