Python cryptography, Rust, and Gentoo

curl backends are largely not pluggable; a given build uses one backend of any given type, and that's it. (Hence a lot of distros ship several curl packages using different crypto backends.)

So it's easy to avoid rust usage in curl on platforms that don't support it: build in some other choice of backends that aren't implemented in Rust. Working on embedded systems with harsher constraints is why a lot of these backends exist in the first place (e.g. the mbedtls backend), so this is nothing new for curl.