* The [docs](https://doc.rust-lang.org/cargo/reference/build-scripts.html#rerun-if-env-changed) suggest that even `build.rs` is may not be a solution:

> Note that the environment variables here are intended for global environment variables like CC and such, **it is not possible to use this for environment variables like TARGET that Cargo sets for build scripts**. The environment variables in use are those received by cargo invocations, not those received by the executable of the build script.

(emphasis mine)

I can't be the only person trying to build a platform-agnostic solution...   Are there _any_ solutions to this within the `cargo` build system (`build.rs` included)?