[llvm] [IR] Add intrinsics to represent complex multiply and divide operations (PR #68742)

[Eli Friedman via llvm-commits]

efriedma-quic wrote:

Do we care whether the results of complex multiply/divide are correctly rounded?  This isn't mentioned anywhere, but the naive expansion double-rounds the result.  And if we use FMA, we still double-round, but produce a different result in some cases.  (If we don't care, that's fine, I guess, but we should explicitly state the expected precision somewhere.)

How does this interact with strictfp?  Do we need separate strictfp intrinsics?

https://github.com/llvm/llvm-project/pull/68742