Add various changes to sconfig and configure.

- Modify the features used by OpenBSD (not everything was
  tested). Mostly copied from Linux, FreeBSD and NetBSD.
- Add support for Bitrig, a fork of OpenBSD. Eventually
  they will differ more and more from OpenBSD.
- Typos and extra trailing spaces.
- Update config.guess and config.sub from GNU.
remove accidentally re-added "native-pkgs"