C++ interop and swig

I see in the top-level README.md that there is no support at the moment for C++ interop. However, I also see that there *is* support for cgo.

What work is required to properly compile .swigcxx files in a package?

I'm hacking together a workaround for the package I'm using, but I'm willing to do this properly and submit a PR. Any pointers about the "right" way to do this?

Read the top-level README.md and the existing cgo support first, then trace how a package’s .swigcxx files are currently handled. Done means the required C++/SWIG interop behavior is defined and package compilation works, with a clear way to validate it.

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