[llvm] [lit] Fix to make "RUN: env PATH=..." work as intended (PR #165308)

[Aiden Grossman via llvm-commits]

https://github.com/boomanaiden154 commented:

> (or find ways to limit it to Linux or something).

I would try to see if it "just works", at least on premerge CI. If something breaks, you can split it out into a separate test file (see the `shtest-ulimit-nondarwin.py`/`shtest-ulimit.py` for an example of the split).

https://github.com/llvm/llvm-project/pull/165308