[compiler-rt] [llvm-lit] Fix Command Not Found Errors in compiler-rt when using lit internal shell (PR #102197)

[Paul Kirth via llvm-commits]

https://github.com/ilovepi approved this pull request.

This seems like a straight forward cleanup. I'd drop the full error message from the description (a summary describing the error is fine. I'd also avoid the use of "I" in the patch, and just describe what you've done. Alternatively, you can use "we".

I'd also retitle to `[llvm-lit][NFC] Replace environment variable with %t`

https://github.com/llvm/llvm-project/pull/102197