rustc: Don't try to write symbols into the metadata for nullary tags. Puts out burning tinderbox.

Author: pcwalton

src/comp/middle/metadata.rs

@@ -369,7 +369,9 @@ fn encode_tag_variant_info(@trans.crate_ctxt cx, &ebml.writer ebml_w,
         encode_kind(ebml_w, 'v' as u8);
         encode_tag_id(ebml_w, did);
         encode_type(ebml_w, trans.node_ann_type(cx, variant.node.ann));
-        encode_symbol(cx, ebml_w, variant.node.id);
+        if (_vec.len[ast.variant_arg](variant.node.args) > 0u) {
+            encode_symbol(cx, ebml_w, variant.node.id);
+        }
         encode_discriminant(cx, ebml_w, variant.node.id);
         ebml.end_tag(ebml_w);
     }