kill: fix GNU compatibility tests for RTMIN and RTMAX

[karanabe]

GNU tests/misc/kill expects kill -l to list RTMIN and RTMAX on Linux and to accept unnamed signal numbers in the listed range.

This change adds list-specific signal helpers in uucore and uses them in kill list/table output and env's __ALL__ expansion. Signal delivery behavior is unchanged.

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/date/resolution (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/misc/kill is no longer failing!
Congrats! The gnu test tests/seq/seq-epipe is now passing!

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/tail/truncate. tests/tail/truncate is passing on 'main'. Maybe you have to rebase?
Skip an intermittent issue tests/tail/symlink (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/date/resolution (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/tty/tty-eof (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/misc/kill is no longer failing!
Note: The gnu test tests/expand/bounded-memory is now being skipped but was previously passing.
Congrats! The gnu test tests/seq/seq-epipe is now passing!

[github-actions]

GNU testsuite comparison:

Congrats! The gnu test tests/misc/kill is no longer failing!
Note: The gnu test tests/cp/link-heap is now being skipped but was previously passing.
Congrats! The gnu test tests/seq/seq-epipe is now passing!

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/date/date-locale-hour (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/misc/kill is no longer failing!
Note: The gnu test tests/cp/link-heap is now being skipped but was previously passing.
Note: The gnu test tests/expand/bounded-memory is now being skipped but was previously passing.

[sylvestre]

well done btw :)

[karanabe]

Thanks!