[compiler-rt] [compiler-rt] Use locally configured llvm-lit for standalone builds (PR #83178)

[Fangrui Song via llvm-commits]

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

The actual mechanism isn't very clear to me, but this and the follow-up does make `check-asan check-msan ...` pass for my standalone build.

https://github.com/llvm/llvm-project/pull/83178