Opaque Pointers

[willtunnels]

As of LLVM 15, LLVM is moving away from typed pointers and toward the use of opaque pointers. These are already supported in LLVM, though, for the time being, typed pointers are also still supported. You can read about this decision and the reasoning behind it here: https://llvm.org/docs/OpaquePointers.html.

We should evolved the Inkwell API to reflect this. At a minimum (and maybe this is all that needs to be done) we need:

• A ptr_type function on Context
• An is_opaque function on PointerType

We also might consider a deprecation warning in LLVM 15+ on typed pointer methods.