[llvm] [lit] Use provided streams in builtin diff (PR #204869)

[Prasoon Kumar via llvm-commits]

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prasoon054 wrote:

Sorry about that! The issue was `import lit.util as util` silently picking up a system-installed `lit` package (which lacks `abs_path_preserve_drive`) instead of the local one from PYTHONPATH. Fixed in https://github.com/llvm/llvm-project/pull/206723 by switching to `from .. import util`. Could you check if this fixes the bot?

https://github.com/llvm/llvm-project/pull/204869