[llvm] [llvm-lit] Precommit Tests for implementing the `unset` command in lit internal shell (PR #104618)

[James Henderson via llvm-commits]

https://github.com/jh7370 commented:

Honestly, I'm not sure this is necessary. `env -u` is a standard Linux shell command, so in theory at least, it should be as well known as `unset` for those used to that style. I think the fact that only two tests use it, and both of those tests are linked tightly, shows that `unset` isn't something people tend to use, so the cost of extra complexity in lit (by virtue of having more code) doesn't really seem justified.

https://github.com/llvm/llvm-project/pull/104618