Add placeholder for cbindgen proc_macro_attribute

wasi-common-cbindgen/src/lib.rs

@@ -0,0 +1,18 @@
+extern crate proc_macro;
+
+use proc_macro::TokenStream;
+use quote::quote;
+use syn::{FnArg, ArgCaptured, Pat, PatIdent};
+use std::collections::HashMap;
+
+#[proc_macro_attribute]
+pub fn wasi_common_cbindgen(attr: TokenStream, function: TokenStream) -> TokenStream {
+    assert!(attr.is_empty());
+
+    let function = syn::parse_macro_input!(function as syn::ItemFn);
+    let result = quote! {
+        #function
+    };
+
+    result.into()
+}