[llvm] [clang-tools-extra] [MLGO] Upstream the corpus extraction tooling (PR #72319)

[Mircea Trofin via cfe-commits]

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+# Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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mtrofin wrote:

Ack - thanks for clarifying the directory structure; looking around, there doesn't seem to be much of a precedent either; so... how about `llvm/utils/mlgo-utils/mlgo`? 

(tests moving to lit sounds perfect)

https://github.com/llvm/llvm-project/pull/72319