Add resolution for extern function items

Author: philberty

gcc/rust/resolve/rust-ast-resolve-item.h

@@ -619,7 +619,7 @@ class ResolveExternItem : public ResolverBase
 
 private:
   ResolveExternItem () : ResolverBase (UNKNOWN_NODEID) {}
-}; // namespace Resolver
+};
 
 } // namespace Resolver
 } // namespace Rust

gcc/rust/resolve/rust-ast-resolve.cc

@@ -637,7 +637,9 @@ ResolveItem::resolve_impl_item (AST::InherentImplItem *item,
 
 void
 ResolveItem::resolve_extern_item (AST::ExternalItem *item)
-{}
+{
+  ResolveExternItem::go (item);
+}
 
 } // namespace Resolver
 } // namespace Rust