wasi: fix warnings

[cakebaker]

This PR fixes some warnings that show up in the wasi job. See, for example, https://github.com/uutils/coreutils/actions/runs/23898299309/job/69688858252?pr=11598#step:18:209

Update: I didn't fix the warnings in fsext.rs because they are fixed in #11568

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/tail/inotify-dir-recreate (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/tty/tty-eof (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/tail/retry is no longer failing!
Note: The gnu test tests/csplit/csplit-heap is now being skipped but was previously passing.

[sylvestre]

oh cool
thanks
we should break the builds when they happen

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/misc/io-errors. tests/misc/io-errors is passing on 'main'. Maybe you have to rebase?
Skipping an intermittent issue tests/cut/bounded-memory (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/date/date-locale-hour (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/tty/tty-eof (passes in this run but fails in the 'main' branch)
Note: The gnu test tests/unexpand/bounded-memory is now being skipped but was previously passing.

[cakebaker]

Waiting with this PR until the wasi-related PRs are merged as they already fix some of the warnings.