Not really? You just need to define the stable ABI: you do that via `[repr(C)]` and other FFI stuff that has been around since essentially the beginning. Then it handles it just fine, for both the code using a runtime library and for writing those runtime libraries.
People writing Rust generally prefer to stay within Rust though, because FFI gives up a lot of safety (normally) and is an optimization boundary (for most purposes). And those are two major reasons people choose Rust in the first place. So yeah, most code is just statically compiled in. It's easier to build (like in all languages) and is generally preferred unless there's a reason to make it dynamic.
People writing Rust generally prefer to stay within Rust though, because FFI gives up a lot of safety (normally) and is an optimization boundary (for most purposes). And those are two major reasons people choose Rust in the first place. So yeah, most code is just statically compiled in. It's easier to build (like in all languages) and is generally preferred unless there's a reason to make it dynamic.