Expose macro_export in guest-rust-macro (#431)

* Expose MacroExport option

* Add MacroExport to Parse func

Author: AmitPr

crates/guest-rust-macro/src/lib.rs

@@ -15,6 +15,7 @@ mod kw {
     syn::custom_keyword!(unchecked);
     syn::custom_keyword!(no_std);
     syn::custom_keyword!(raw_strings);
+    syn::custom_keyword!(macro_export);
     syn::custom_keyword!(macro_call_prefix);
     syn::custom_keyword!(export_macro_name);
     syn::custom_keyword!(skip);
@@ -24,6 +25,7 @@ enum Opt {
     Unchecked,
     NoStd,
     RawStrings,
+    MacroExport,
     MacroCallPrefix(LitStr),
     ExportMacroName(LitStr),
     Skip(Vec<LitStr>),
@@ -41,6 +43,9 @@ impl Parse for Opt {
         } else if l.peek(kw::raw_strings) {
             input.parse::<kw::raw_strings>()?;
             Ok(Opt::RawStrings)
+        } else if l.peek(kw::macro_export) {
+            input.parse::<kw::macro_export>()?;
+            Ok(Opt::MacroExport)
         } else if l.peek(kw::macro_call_prefix) {
             input.parse::<kw::macro_call_prefix>()?;
             input.parse::<Token![:]>()?;
@@ -68,6 +73,7 @@ impl wit_bindgen_rust_macro_shared::Configure<Opts> for Opt {
             Opt::Unchecked => opts.unchecked = true,
             Opt::NoStd => opts.no_std = true,
             Opt::RawStrings => opts.raw_strings = true,
+            Opt::MacroExport => opts.macro_export = true,
             Opt::MacroCallPrefix(prefix) => opts.macro_call_prefix = Some(prefix.value()),
             Opt::ExportMacroName(name) => opts.export_macro_name = Some(name.value()),
             Opt::Skip(list) => opts.skip.extend(list.iter().map(|i| i.value())),