readdir_r is not POSIX according to POSIX_SOURCE, bruce says:
> readdir_r() is in the _POSIX_SOURCE section, but is not a POSIX.1-1990
> function. It's POSIX.1-1996 so it should be under a different feature
> test which we don't support yet.
make sure errno is saved so that its contents are cleared unless
necessary.
Submitted by: bde