[llvm] [Support] Show '[subcommand]' in the help for less than 3 subcommands (PR #74557)

[Igor Kudrin via llvm-commits]

igorkudrin wrote:

> LGTM. Strange that the original patch ([79f3333](https://github.com/llvm/llvm-project/commit/79f3333d3f04c26cde06a663dca7b79e1ac86345)) used `> 2` for "at least 1". I wonder if some refactoring later caused the issue?

Thanks. I guess that it was made to match the condition `(Sub == &*TopLevelSubCommand && Subs.size() > 2)` a few lines later. And (just guessing again) the original idea about `Subs.size() > 2` might have been based on the assumption that two special subcommands, `TopLevel` and `All`, would also be added to the list. And all this proves once again the importance of testing.

https://github.com/llvm/llvm-project/pull/74557