fix(libc): keep EINVAL from strerror_r for an unknown error with a short buffer

[fma-rc]

What

strerror_r with an unknown error number and a buffer too small for the "Unknown error: N" text returned ERANGE (34). FreeBSD 11 returns EINVAL (22) for an unknown number whatever the buffer size: in lib/libc/string/strerror.c (releng/11.4) the errnum < 0 || errnum >= sys_nerr branch sets retval = EINVAL and only the known-number branch can set ERANGE. The text is still written truncated, as before.

One line in Errors.cpp, two assertions in guest_errors. #2057 made the same change and was closed by its author before review; this is a fresh patch on current main.

Tested

Arch Linux, GCC 16.2.1, Release, main d2f43cb. guest_errors with only the new assertions aborts; with the fix it passes 5 of 5. No GPU involved. python3 tools/check_conventions.py --base origin/main passes. Not tested on Windows.

Checklist

• Based on current main; no other open PR implements the same functions
• One topic per PR; follow-ups go in a new PR
• No comments in code except technical debt
• Unimplemented paths throw (NotImplemented_nid_no_patch); silent stubs are listed in TechnicalDebt
• No notes, investigation .md files or images added to the repository (attach them to this PR)
• New third-party code is a submodule built from source
• Generic behaviour, not specific to one title
• Depends on: none
• AI-assisted: yes

[github-actions]

Thank you for your interest in the project! We are sorry, but we cannot accept more PRs while we work through the existing backlog. This PR has been automatically closed and labeled "intake paused". This is not a judgment of the quality of your changes.

[adriadam10]

Checked against FreeBSD releng/11.4 strerror.c (EINVAL for unknown numbers, ERANGE only in the known-number branch); guest_errors passes and fails without the change on a Linux build. Merging.