[compiler-rt] [compiler-rt][test] Move tmp dir creation with env to where dir is run (PR #106252)

[Petr Hosek via llvm-commits]

petrhosek wrote:

> > Is the test failing with your change?
> 
> @petrhosek Yes, it does. It was also failing before this change when run with lit's internal shell due to the `env` command not having a subcommand.

What's the failure?

https://github.com/llvm/llvm-project/pull/106252