[llvm] [DAGCombiner] Fold freeze(fmul) + fadd/fsub into FMA combine (PR #142250)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

By the looks of it SelectionDAG::canCreateUndefOrPoison doesn't handle fp ops at all - should we start with fixing those to more closely match ValueTracking llvm::canCreateUndefOrPoison?

https://github.com/llvm/llvm-project/pull/142250