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