wasi: add all _SC_* sysconf constants from wasi-libc

[surban]

Description

Add the complete set of _SC_* sysconf constants for WASI targets from wasi-libc's musl-based unistd.h.

Applies to both wasm32-wasip1 and wasm32-wasip1-threads.

Sources

• wasi-libc musl unistd.h: https://github.com/WebAssembly/wasi-libc/blob/2fc32bc81b9f07f8d9525edea59bfbaf760c06d6/libc-top-half/musl/include/unistd.h#L396

Checklist

• Relevant tests in 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

[Copilot]

Pull request overview

This PR expands the WASI target’s exported sysconf name constants in src/wasi/mod.rs and updates the WASI semver symbol list accordingly, improving libc API completeness for WASI consumers.

Changes:

• Added a broad set of _SC_* sysconf selector constants for the WASI target.
• Updated libc-test/semver/wasi.txt to include the newly exported WASI symbols.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/wasi/mod.rs	Adds WASI _SC_* constants (sysconf name IDs) to the WASI libc surface.
libc-test/semver/wasi.txt	Records the new WASI symbols in the semver baseline list.

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[surban]

@rustbot retry