[NativeAOT-LLVM] Fix up LSSA logging around liveness

[SingleAccretion]

The current (a bit lazy) logic is not correct as uncovered by Yowl, since it runs before PHIs are processed. Reproduction:

[MethodImpl(MethodImplOptions.NoInlining)]
private static unsafe object Problem(object x, object y)
{
    object z = x != null ? y : x;
    Use(&z);
    return z;
}

public static unsafe void Use<T>(T* arg) { }