[llvm] [InstSimplify] Move Select with bittest folds. NFC. (PR #122944)

[Nikita Popov via llvm-commits]

https://github.com/nikic commented:

In terms of general approach, could you please land https://github.com/llvm/llvm-project/pull/122179, add trunc support to it, and *then* update folds together with added test coverage for the change?

https://github.com/llvm/llvm-project/pull/122944