Support renameat2 and statx under musl libc

[frc4533-lincoln]

Description

This PR enables statx and adds renameat2 under musl libc.

Sources

• renameat2: https://github.com/bminor/musl/blob/ae3a8c93a663b553e65f096498937083dad210d2/include/stdio.h#L166
• statx: https://github.com/bminor/musl/blob/ae3a8c93a663b553e65f096498937083dad210d2/include/sys/stat.h#L108

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

[tgross35]

Statx was added in ef3c046. Could you drop the statx changes and do something similar with that config for renameat2?