- Do not probe paths that do not exist (ENOENT).
- If the OS supports open()ing directories (HAVE_FDOPENDIR), do not
  probe paths that cannot be opened.
- Do not probe files whereby fstat() fails.
- Do not probe non-regular files other than directories and block
  devices (previously, only FIFOs were discarded).
- Look for anchor even if fstat() is not supported.

Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>

Signed-off-by: Felix Paul Kühne <fkuehne@videolan.org>

See http://forum.videolan.org/viewtopic.php?f=14&t=90169

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

It makes sense, especially since the libav/FFmpeg split

Also, __USE_UNIX98 is a libc-internal definition. The build system is
not supposed to define that directly (we have _GNU_SOURCE).

(Note __BUILTIN__ was not used anymore as we have !__PLUGIN__)