Hermetic C++ Toolchain example

Setting up an actual hermetic c/c++ toolchain is quite an involved exercise. I understand it's a big task, but it would be a great benefit to adopters to have a guide on how to achieve this and I'd love to see it on the roadmap. The provided zig toolchain isn't suitable for a lot of usecases, and I can see a need for users to create a hermetic clang toolchain using clang & either the system glibc or one pulled from an artifact/committed more directly