wc: respect POSIXLY_CORRECT for word counting

[dhr412]

Closes #10321
Should I add a test as well?

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/shuf/shuf-reservoir (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/sort/sort-stale-thread-mem (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/ptx/ptx-overrun is no longer failing!

[sylvestre]

Yes for tests. It is rare that we accept a pr without it

[codspeed-hq]

CodSpeed Performance Report

Merging this PR will degrade performance by 4.44%

_{Comparing dhr412:posix-corr-wc (db7d458) with main (6381266)}

Summary

⚡ 1 improved benchmark
❌ 1 regressed benchmark
✅ 280 untouched benchmarks
⏩ 38 skipped benchmarks¹

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

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Memory	sort_key_field[500000]	31.4 MB	32.8 MB	-4.44%
⚡	Memory	du_wide_tree[(5000, 500)]	1.3 MB	1.2 MB	+7.39%

Footnotes

1. 38 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:

Skipping an intermittent issue tests/shuf/shuf-reservoir (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/sort/sort-stale-thread-mem (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/ptx/ptx-overrun is no longer failing!

[cakebaker]

Thanks!