mkfifo: replace unsafe libc::mkfifo with nix::unistd::mkfifo

[sylvestre]

No description provided.

[codspeed-hq]

CodSpeed Performance Report

Merging this PR will not alter performance

_{Comparing sylvestre:mkfifo-nix (23fed67) with main (2e26454)¹}

Summary

✅ 142 untouched benchmarks
⏩ 37 skipped benchmarks²

Footnotes

1. No successful run was found on main (23b11ea) during the generation of this report, so 2e26454 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

2. 37 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/tty/tty-eof (passes in this run but fails in the 'main' branch)