[clang] [clang] constexpr built-in fma function. (PR #113020)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> I suspect fma is not one of the functions we want to try to share, at least not short-term. It's one of the core IEEE operations, LLVM has APFloat::fusedMultiplyAdd since forever, and there's probably some weirdness with dependencies if we try to share it because other operations use it.

That's fair, I don't insist on sharing here, but it is something we should be planning for with the wider set of changes IMO.

https://github.com/llvm/llvm-project/pull/113020