[llvm] [llvm][llvm-lit] Hide --use-unique-output-file-name from --help (PR #114812)

[David Spickett via llvm-commits]

DavidSpickett wrote:

> Has there been some opposition to the option being public, or was your intention always for it to be internal to LLVM only?

It's a bit of both, I shouldn't have merged it as soon as I did. My intention was that it would be broadly useful but at this time there is only one known user of it, which would be us i the Buildkite CI.

This was raised on follow up patches: https://github.com/llvm/llvm-project/pull/113447#issuecomment-2435906275

My survey of use on GitHub showed that while it has been a problem for external lit users, they have usually solved it by refactoring the pipeline which brings other benefits with it (https://github.com/llvm/llvm-project/pull/113447#issuecomment-2443731763). This is something LLVM should do as well, but I'm told we may be moving the CI soon, so if I want to improve things in the short term I needed something low impact.

I went through a bunch of alternatives that didn't need a new option, but there was only one other viable option which is wrapping lit in another script. Small chance we go with that and I revert the option altogether, still waiting for confirmation either way on that.

So this time I will not be so hasty merging this :)

If this goes ahead, my plan would be to remove this option as soon as LLVM's own CI does not need it. Hiding it means if it ends up in lit 20.1.0 then we have done as much as we can to make sure external users don't rely on it.

https://github.com/llvm/llvm-project/pull/114812