The `kani` library doesn't get linked to goto binaries

[tedinski]

This was previously invisible because we either (1) had codegen hooks, so we replaced calls during codegen, or (2) were generic, and so got monomorphized into dependent crates.

But as soon as we add a normal symbol, no generics and no codegen hook, you'd see missing symbol errors because we never get a symtab.json from kani and link it into generated goto binaries.