fix: value of PTHREAD_MUTEX_DEFAULT on illumos

[Berrysoft]

Description

The value on illumos is different to the one on solaris.

Sources

https://github.com/illumos/illumos-gate/blob/master/usr/src/head/pthread.h

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]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @tgross35 (or someone else) some time within the next two weeks.

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[rustbot]

Some changes occurred in solarish module

cc @jclulow, @pfmooney

[pfmooney]

Please see the commentary on this value in #4023.

[Berrysoft]

Fair enough:)