feat(c-api) Use our fork of cbindgen.

Our fork contains incoming PR. It helps for example to skip struct
fields.

lib/c-api/src/wasm_c_api/instance.rs

@@ -10,6 +10,7 @@ use wasmer::{Extern, Instance};
 
 #[repr(C)]
 pub struct wasm_instance_t {
+    /// cbindgen:ignore
     pub(crate) inner: Arc<Instance>,
 }