sort: allow -f to be pass multiple time

[just1602]

Hello 👋

This small PR try to fix #5667.

I'm pretty new to rust, so if there's a better way to allow a flag to be pass multiple time, let me know. 😄

echo "foo" | target/debug/sort -f -f
foo

[tertsdiepraam]

Thanks! Yeah, there is a better way, although you would've needed to know clap pretty well to find it 😄 You can check out this PR as an example: #5671. As a bonus it will work for all arguments if we do it that way.

[tertsdiepraam]

See comment above

[sylvestre]

and with a test to make sure we don't regress please :)

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/tail/inotify-dir-recreate

[tertsdiepraam]

Excellent!