Python cryptography, Rust, and Gentoo

> When you cross-build something for another target, you'd just install the libc headers for that other target, yes! I don't see why you wouldn't.

Because that makes cross-compilation harder and more fragile. LLVM-based environments typically have all the code generation capabilities for every platform available through the same binary and toolchain. Having to install a specific cross-libc, and having the capabilities of the libc crate depend on your installed libc headers, would make cross-compilation harder, less reproducible, and more fragile.

This doesn't mean we can't do code generation based on those headers, but we'd want to ship either the headers or the generated code with the libc crate.