Finally, some good news. After three months of work, which included writing from scratch a new, powerful transformational system called Piggy, the SWIG-generated CUDA interface that Campy used has been removed, and a Piggy-generated CUDA interface substituted in its place. A release of Piggy was added to NuGet, which contains the Clang AST serializer, the Piggy tool, a basic set of templates, and the build rules to call the tool on the fly in a C# project. As a bonus, due to the fact that the dependency is directly on the CUDA drivers (nvcuda.dll), and not the NVIDIA GPU Computing Toolkit, nothing is needed beyond the drivers for the graphics card, unless you intend to build Campy itself from scratch. So, Campy is CUDA 10/9/8 (and probably earlier versions)
Sometimes small steps are the most difficult. But, with this fix, I can move onto fixing the SWIG wrapper for LLVM, and then finally back on Campy. After this, I intend to start rewriting much of the native code in the Net Core runtime in order for it to be completely platform independent. Once that is done, C# should be portable to any CPU or GPU.