feat(c-api) Make wasi_config_t and wasi_env_t opaque structures.

Removing `repr(C)` make them opaque for cbindgen. Which is perfect for what we want.

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

@@ -11,5 +11,6 @@ pub mod store;
 pub mod trap;
 pub mod types;
 pub mod value;
+
 #[cfg(feature = "wasi")]
 pub mod wasi;

lib/c-api/src/wasm_c_api/wasi/mod.rs

@@ -26,7 +26,6 @@ use wasmer_wasi::{
 
 #[derive(Debug, Default)]
 #[allow(non_camel_case_types)]
-#[repr(C)]
 pub struct wasi_config_t {
     inherit_stdout: bool,
     inherit_stderr: bool,
@@ -91,7 +90,6 @@ pub extern "C" fn wasi_config_inherit_stdin(config: &mut wasi_config_t) {
 }
 
 #[allow(non_camel_case_types)]
-#[repr(C)]
 pub struct wasi_env_t {
     /// cbindgen:ignore
     inner: WasiEnv,