Mystery of the `clib` and `inwelling` crates

I'm trying to use the tcl crate, which provides bindings for the Tcl programming language. However, I get compile errors from the crate not generating the raw bindings during build time that it uses to provide the higher-level bindings, even though I have Tcl and the associated C library installed and pkgconf can find them. Looking into the code, it uses the clib crate from the same author to generate the bindings. In its build.rs, it uses metadata from its dependencies and uses them to figure ...