[llvm] [InstCombine] Add combines for `(icmp eq/ne (and X, P2), (and X, -P2))` (PR #94867)

[Nikita Popov via llvm-commits]

https://github.com/nikic commented:

> If P2 is not constant, then we only perform the fold if the and
ops are multi-use. This, however, saves an instruction compared to the
xor + and variant.

Unless this also came up in the diffs, please remove it from this PR.

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A possible alternative way to handle the motivating cases would be to allow the fold if X and Y are constants and only one of the ands is one-use. This is better in some ways (handles *any* constants) and worse in others (does not handle both ands being multi-use).

https://github.com/llvm/llvm-project/pull/94867