e4defrag: choose the best available posix_fadvise variant

e4defrag: choose the best available posix_fadvise variant

Use posix_fadvise64() when available.  This allows 64bit offsets on
32bit systems.

[ Modified by tytso to try to use fadvise64() as well, and to remove
  the attempt to call the syscall directly, since because and
  complexities caused by required dummy arguments on some
  architectures, it's not worth the hair.  ]

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>