[llvm] [SelectionDAG] Optimize zero-extended multiplies on targets without native LOHI mul (PR #203135)

[Timothy Herchen via llvm-commits]

anematode wrote:

Nice! :) Definitely fixes the WASM use case that I had in mind, but not familiar with the other arches, so can't comment there

https://github.com/llvm/llvm-project/pull/203135