Make structopt-derive available to product and vendor

Bug: 270690570

Test: mma in external/rust/crates
Change-Id: I1888b77446ba31175d33d060d1e849b25d3df996
diff --git a/Android.bp b/Android.bp
index 9e35e36..14e9eb0 100644
--- a/Android.bp
+++ b/Android.bp
@@ -41,6 +41,7 @@
 
 rust_proc_macro {
     name: "libstructopt_derive",
+    // has rustc warnings
     crate_name: "structopt_derive",
     cargo_env_compat: true,
     cargo_pkg_version: "0.4.18",
@@ -53,4 +54,6 @@
         "libquote",
         "libsyn",
     ],
+    product_available: true,
+    vendor_available: true,
 }