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

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

SelectionDAG::canCreateUndefOrPoison checks for hasPoisonGeneratingFlags - which seems to cover nonans/noinfs - but we'd definitely need to have test coverage for this.

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