redox: more sysconf constants

[willnode]

Description

This PR is a part of effort to introduce uutils nproc which requires constants _SC_NPROCESSORS_CONF and _SC_NPROCESSORS_ONLN. I see that there's other sysconf constants that's not updated here so I add them too.

Sources

• Relibc constants
• merged SC_NPROCESSORS_* implementation

Checklist

• Relevant tests in libc-test/semver have been updated
• No placeholder or unstable values like *LAST or *MAX are
  included (see #3131)
• Tested locally (cd libc-test && cargo test --target mytarget);
  especially relevant for platforms that may not be checked in CI