[llvm] CodeGen: Add -denormal-fp-math-bf16 flag (PR #90425)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> I'm afraid so. BF16 instructions belong to two CPUIDs of AVX512_BF16 and AVX_NE_CONVERT. E.g.
> 

Is it all the operations, or just these specific dot products? Are there specific bf16<->float conversions that have the same issue? What about basic arithmetic operations?

https://github.com/llvm/llvm-project/pull/90425