[llvm] [ValueTracking] Analyze `Select` in `isKnownNonEqual`. (PR #68427)

[Mikhail Gudim via llvm-commits]

mgudim wrote:

@nikic @goldsteinn I added a new commit moving the `isNonEqualSelect` to the end of `isKnownNonEqual`.

This is necessary so that we can analyze things like
`isKnownNonEqual(X, Y)` where `X = select ... ` and `Y = shl X, 2` for
example. In other words, we first should try to do the analysis without
"decomposing" `select`. If that doesn't succeed then we try `isNonEqualSelect`.

https://github.com/llvm/llvm-project/pull/68427