sync: fix exit code when fcntl failed & 2>/dev/full abort

[oech3]

Closes #11507

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/misc/coreutils. tests/misc/coreutils is passing on 'main'. Maybe you have to rebase?
Skip an intermittent issue tests/date/resolution (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/date/date-locale-hour (passes in this run but fails in the 'main' branch)
Note: The gnu test tests/dd/no-allocate is now being skipped but was previously passing.
Note: The gnu test tests/printf/printf-surprise is now being skipped but was previously passing.
Congrats! The gnu test tests/cp/link-heap is now passing!
Note: The gnu test tests/misc/write-errors was skipped on 'main' but is now failing.

[codspeed-hq]

Merging this PR will not alter performance

✅ 303 untouched benchmarks
⏩ 46 skipped benchmarks¹

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_{Comparing oech3:sync-abort (690131e) with main (aab0dda)}

Footnotes

1. 46 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:

GNU test failed: tests/misc/io-errors. tests/misc/io-errors is passing on 'main'. Maybe you have to rebase?
Skip an intermittent issue tests/pr/bounded-memory (fails in this run but passes in the 'main' branch)
Congrats! The gnu test tests/cp/link-heap is now passing!
Note: The gnu test tests/misc/write-errors was skipped on 'main' but is now failing.

[github-actions]

GNU testsuite comparison:

Note: The gnu test tests/tail/tail-n0f is now being skipped but was previously passing.