[llvm] [DAGCombiner] Combine frem into fdiv+ftrunc+fma (PR #67642)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> I tested with a number of random floating values. In most of the cases, the expanded result is exactly the same as libcall result.
> 
> But when `fmod(a,b)` is very close to `b` (smaller than `1e-10`, for example, `fmod(521862.045173469, 31.048432006988875)`), the result would be totally wrong.. I'm thinking about a solution.

I am interested an in inline expansion of frem that is 100% correct, but I think this is fine for afn 

https://github.com/llvm/llvm-project/pull/67642