[InstSimplify] Forbid undef folds in expandBinOp

This is the replacement for D84250 based on D84792. As we recursively
fold with the same value twice, we need to disable undef folds,
to prevent an undef from being folded to two different values.

Reverting rG00f3579a and using the
test case from https://reviews.llvm.org/D83360#2145793, it no longer
performs the incorrect fold.

Differential Revision: https://reviews.llvm.org/D85684