[llvm] [ConstraintElim] Add facts implied by llvm.abs (PR #73189)

[Florian Hahn via llvm-commits]

fhahn wrote:

LGTM, thanks!

> p.s. clang-format doesn't seem to format "if" properly: <img alt="Screenshot 2023-12-28 at 11 35 33 PM" width="742" src="https://private-user-images.githubusercontent.com/6532716/293326872-e0d9e0a5-2556-4901-bf7a-0bb5dbeb87e0.png?jwt=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.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.xewzNzfz7D8K91RQsxgIgj9EyWp58by6LRg4m4cEQ1U">

having multiple statements in an `if` is very uncommon in the codebase I think and should probably be avoided for consistency.

https://github.com/llvm/llvm-project/pull/73189