df: df-output.sh fails because of error message generated by clap

[cakebaker]

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df-output.sh (from the GNU coreutils test suite) tests, for example, whether df -i --output causes a "mutually exclusive options" error and shows a corresponding error message.

With uutils df, clap is used to handle mutually exclusive options. And it generates an error message that's different than what the GNU coreutils test suite expects.

I see two ways to resolve this issue: simply ignore df-output.sh, or handle mutually exclusive options manually without clap.

[tertsdiepraam]

There is a third option (which I prefer in this case), which is to replace the text that GNU expects with the text we print. We've already done this for a few utils at the end of util/build-gnu.sh.

[cakebaker]

Fixed in https://github.com/uutils/coreutils/pull/5452