[compiler-rt] [llvm-lit] Fix error in compiler-rt tests when using lit internal shell with env (PR #102069)

[Paul Kirth via llvm-commits]

ilovepi wrote:

> `VAR=a command` is so commonly used that perhaps the internal lit shell should be taught this syntax. Then we can avoid these changes.

While I think it would be nice if `llvm-lit` handled this more gracefully, its already has a standard way to handle this via `env`, which I think (and forgive me if I'm mistaken here) works better w/ older shells, like `sh`, `csh`, `ksh`, etc.  Plus, `env` is already used pretty pervasively across LLVM, so I'm not seeing how this change isn't desirable on its own,  especially given that it allows the tests to run in more environments. 

You noted in https://discourse.llvm.org/t/rfc-enabling-the-lit-internal-shell-by-default/80179/20 that some improvements to `llvm-lit` aren't essential to change the default. This type of test fixing would seem to fall under that. If you feel strongly about your POV, then we should probably move the discussion to the RFC thread on discourse to solicit more feedback from the community.

https://github.com/llvm/llvm-project/pull/102069