This extends the optimisation implemented in #107769 by relaxing the
condtions to make it happen. Now, the value produced by `ucmp`/`scmp`
doesn't need to be one-use, but only one-user, meaning it can be present
in a single phi node more than once.
When we have a `phi` instruction with more than one of its incoming
values being a call to `ucmp` or `scmp`, which is then compared with an
integer constant, we can move the comparison through the `phi` into the
incoming basic blocks because we know that a comparison of `ucmp`/`scmp`
with a constant will be simplified by the next iteration of InstCombine.
There's a high chance that other similar patterns can be identified, in
which case they can be easily handled by the same code by moving the
check for "simplifiable" instructions into a lambda.
