FFI: Create ffi Cargo feature and include ffi module.

Cargo.toml

@@ -13,10 +13,12 @@ crate-type = ["lib", "cdylib", "staticlib"]
 
 [features]
 use_tolk = ["tolk"]
+ffi = ["libc"]
 
 [dependencies]
 dyn-clonable = "0.9"
 lazy_static = "1"
+libc = {version = "0.2", optional = true}
 log = "0.4"
 thiserror = "1"
 

src/lib.rs

@@ -28,6 +28,8 @@ use objc::{class, msg_send, sel, sel_impl};
 use thiserror::Error;
 
 mod backends;
+#[cfg(feature = "ffi")]
+pub mod ffi;
 
 #[derive(Clone, Copy, Debug)]
 pub enum Backends {