Add missing constants from unistd.h for newlib targets

[FenrirWolf]

Description

A new API was recently added to std, and as a result a number of newlib-based targets are failing to build due to a missing definition for _SC_HOST_NAME_MAX from the unistd.h header. This PR adds that missing constant along with a number of other sysconf symbols that never made it into the crate for these targets.

Sources

https://github.com/bminor/newlib/blob/master/newlib/libc/include/sys/unistd.h#L354-L512

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

@rustbot label +stable-nominated

[tgross35]

Thanks for the fix, I have a few small nits here.

Could you also move these constants to src/new/newlib/unistd.rs? We're slowly migrating to a structure that follows the source closer.

[FenrirWolf]

Sure, I moved the definitions and changed them to match the source too.

[tgross35]

LGTM, thank you!

[tgross35]

I'm going through the backports and just FYI, this commit didn't get attributed to you for some reason. Per https://github.com/rust-lang/libc/commit/8a4b635aeae3b68da7ef8c40d190c10a73e30526.patch this was authored by From: = <=>.

Perhaps that is intentional, but figured it's worth letting you know in case it comes from a bad bash env or something :)