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]

GNU testsuite comparison:

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

[github-actions]

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]

GNU testsuite comparison:

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

[codspeed-hq]

CodSpeed Performance Report

Merging #9437 will not alter performance

_{Comparing naoNao89:sync-remove-unwrap (bf57c56) with main (77c3498)}

Summary

✅ 136 untouched
⏩ 6 skipped¹

Footnotes

1. 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]

GNU testsuite comparison:

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

[github-actions]

GNU testsuite comparison:

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

[github-actions]

GNU testsuite comparison:

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

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/tty/tty-eof. tests/tty/tty-eof is passing on 'main'. Maybe you have to rebase?