[llvm] [Attributor] Pack out arguments into a struct (PR #119267)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> @arsenm @shiltian @vidsinghal @jdoerfert @jhuber6 I am sorry but this is my first time with the attributor. I keep getting compilation errors like:
> 
> ```
> error: invalid new-expression of abstract class type ‘{anonymous}::AAConvertOutArgumentFunction’
> 13207 |     AA = new (A.Allocator) CLASS##SUFFIX(IRP, A);
> ```
> 

You didn't implement a virtual method of the base class. If you look further along in the error message it should tell you which ones 

https://github.com/llvm/llvm-project/pull/119267