Tracking issue for `linked_from` feature

Tracks stabilization of the `linked_from` attribute. From the reference

> `linked_from` indicates what native library this block of FFI items is coming from. This attribute is of the form `#[linked_from = "foo"]` where `foo` is the name of a library in either `#[link]` or a `-l` flag. This attribute is currently required to export symbols from a Rust dynamic library on Windows
