[llvm] [InstCombine] Fold selection between less than zero and one (PR #69961)

[via llvm-commits]

XChy wrote:

Just `A pred C ? (A << BW - 1) : 1` --> `Zext(A pred C ? A < 0 : 1)`. The latter form would be automatically folded somewhere else.

https://github.com/llvm/llvm-project/pull/69961