[llvm] Attributor: Add denormal-fp-math to attributor-light (PR #79576)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> I think it's quite unlikely that AttributorLight will become part of the default pipeline anytime soon, especially if more attributes get added to it. 

This should be as cheap as it gets for interprocedural inference and doesn't require inspecting the function contents 

> So if you need this, you do need to implement it in the production FunctionAttrs pass. Unless this is a for a custom, non-upstream pipeline?

At some point I'll probably just switch the default for AMDGPU. I can't wait forever for this switch 

https://github.com/llvm/llvm-project/pull/79576