[llvm] [LV][VPlan] Change the inheritance of class VPWidenSelectRecipe to class VPRecipeWithIRFlags, which allows recipe of the select to pass the fastmath flags (PR #121023)

[Mel Chen via llvm-commits]

https://github.com/Mel-Chen commented:

Don't we need to call setFlags() in execute()?

https://github.com/llvm/llvm-project/pull/121023