stdbuf: Fix cfg block for Cygwin

[oech3]

No description provided.

[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/date/date-locale-hour (passes in this run but fails in the 'main' branch)
Note: The gnu test tests/csplit/csplit-heap is now being skipped but was previously passing.
Congrats! The gnu test tests/basenc/bounded-memory is now passing!
Congrats! The gnu test tests/tail/pipe-f is now passing!

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/date/date-locale-hour (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/pr/bounded-memory (passes in this run but fails in the 'main' branch)
Note: The gnu test tests/seq/seq-epipe is now being skipped but was previously passing.

[Ecordonnier]

Can you please fix the conflicts?

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/date/date-locale-hour (fails in this run but passes in the 'main' branch)

[codspeed-hq]

Merging this PR will degrade performance by 14.62%

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

⚡ 1 improved benchmark
❌ 2 regressed benchmarks
✅ 297 untouched benchmarks
⏩ 46 skipped benchmarks¹

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	Memory	cp_recursive_deep_tree[(120, 4)]	699.2 KB	615.6 KB	+13.59%
❌	Simulation	true_consecutive_calls	170.3 ns	199.4 ns	-14.62%
❌	Simulation	false_consecutive_calls	170.3 ns	199.4 ns	-14.62%

---

_{Comparing oech3:stdbuf-cfg (781ac60) with main (230e0cf)}

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. ↩

[oech3]

@Ecordonnier ready.

[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/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)
Note: The gnu test tests/basenc/bounded-memory is now being skipped but was previously passing.
Note: The gnu test tests/cp/link-heap is now being skipped but was previously passing.
Congrats! The gnu test tests/tail/tail-n0f is now passing!

[oech3]

Too flakey CI. I cannot pass.

[cakebaker]

Thanks!