[llvm] [ConstantFolding] Add support for llvm.atan in constant folding. (PR #143416)

[Joshua Cranmer via llvm-commits]

jcranmer-intel wrote:

> I think the constant folding just calls the native libm function linked with the compiler.

Which we really shouldn't be doing, I know @andykaylor has filed an issue on that in the past. The sooner we can get llvm-libc hand-in-hand with APFloat integration, the better.

https://github.com/llvm/llvm-project/pull/143416