mkfifo: don't delete fifo and fail when --context is used without SELinux/SMACK

[Chaganti-Reddy]

mkfifo currently deletes the fifo it just created and exits with a fatal error if --context is used on a kernel without SELinux/SMACK. same root cause as the mkdir bug, GNU just creates the fifo and warns instead. added the missing branch so it only bails out for real SELinux errors now, not for "not enabled".

Fixes #12983

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/cut/bounded-memory (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/pr/bounded-memory (fails in this run but passes in the 'main' branch)
Congrats! The gnu test tests/expand/bounded-memory is now passing!
Congrats! The gnu test tests/rm/many-dir-entries-vs-OOM is now passing!

[codspeed-hq]

Merging this PR will not alter performance

✅ 172 untouched benchmarks
⏩ 213 skipped benchmarks¹

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_{Comparing Chaganti-Reddy:mkfifo-context-warning (a0a8cb7) with main (ef50d8b)}

Footnotes

1. 213 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. ↩