[llvm] ValueTracking: Use fcAllFlags for unknown value (PR #66393)

[Nikita Popov via llvm-commits]

https://github.com/nikic approved this pull request.

I don't really get when this could matter (if you don't have an operand, then there is nothing the mask could apply to), but I also agree that this is slightly nicer by dint of being the conservative return value.

https://github.com/llvm/llvm-project/pull/66393