sync: Reset O_NONBLOCK flag after file validation to match GNU behavior

[naoNao89]

This PR adds proper flag reset logic to the sync utility to align with GNU coreutils implementation.

Changes

• Reset O_NONBLOCK flag before calling syncfs() and fdatasync()
• Added necessary imports: fcntl, FcntlArg, OFlag, and AsRawFd
• Applies to Linux/Android platforms only

The implementation ensures proper handling of non-blocking file descriptors before performing synchronization operations.

https://www.gnu.org/software/coreutils/manual/html_node/sync-invocation.html

[github-actions[bot]]

GNU testsuite comparison:

Skip an intermittent issue tests/tail/overlay-headers (fails in this run but passes in the 'main' branch)

[github-actions[bot]]

GNU testsuite comparison:

Skip an intermittent issue tests/tail/overlay-headers (fails in this run but passes in the 'main' branch)

[sylvestre]

Could you please add a test for this?

[github-actions[bot]]

GNU testsuite comparison:

Skip an intermittent issue tests/misc/tee (fails in this run but passes in the 'main' branch)

[codspeed-hq[bot]]

CodSpeed Performance Report

Merging #9437 will degrade performances by 2.34%

_{Comparing naoNao89:sync-remove-unwrap (3577f24) with main (415d01c)}

Summary

⚡ 1 improvement
❌ 1 regression
✅ 125 untouched
⏩ 6 skipped[^skipped]

:warning: Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
❌	tsort_input_parsing_heavy[5000]	82.1 ms	84.1 ms	-2.34%
⚡	du_max_depth_balanced_tree[(6, 4, 10)]	33.1 ms	32.4 ms	+2.15%
[^skipped]: 6 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[bot]]

GNU testsuite comparison:

Skip an intermittent issue tests/tail/overlay-headers (fails in this run but passes in the 'main' branch)

[github-actions[bot]]

GNU testsuite comparison:

Skipping an intermittent issue tests/tail/overlay-headers (passes in this run but fails in the 'main' branch)

[github-actions[bot]]

GNU testsuite comparison:

Skipping an intermittent issue tests/tail/overlay-headers (passes in this run but fails in the 'main' branch)