[llvm] [KnownBits] Use min non-zero divisor and quotient lower bound in udiv (PR #209360)

[Jay Foad via llvm-commits]

jayfoad wrote:

I'd appreciate it if you could rewrite the desciption to be much more succinct. Quoting https://llvm.org/docs/AIToolPolicy.html#details:

> To ensure sufficient self review and understanding of the work, it is strongly recommended that contributors write PR descriptions themselves

https://github.com/llvm/llvm-project/pull/209360