[llvm] [DAGTypeLegalize] Legalize ISD::POISON as ISD::UNDEF for Float Type Legalization (PR #135056)

[Jakub Kuderski via llvm-commits]

kuhar wrote:

Reverting the revert would get us back into a broken state. We should reland the original PR with this fix.

https://github.com/llvm/llvm-project/pull/135056