Bug 1173447 - bustage fix followup

MozReview-Commit-ID: IsQ1EtCypX8

--HG--
extra : rebase_source : babc112fdee11d0aef8746d8c2b36d5c3120eb8c

js/src/jsapi-tests/testGCMarking.cpp

@@ -173,9 +173,11 @@ BEGIN_TEST(testIncrementalRoots)
     MOZ_ASSERT(!leafHandle->asTenured().isMarked());
     MOZ_ASSERT(!leafOwnerHandle->asTenured().isMarked());
 
+#ifdef DEBUG
     // Remember the current GC number so we can assert that no GC occurs
     // between operations.
     auto currentGCNumber = rt->gc.gcNumber();
+#endif
 
     // Now do the incremental GC's worst nightmare: rip an unmarked object
     // 'leaf' out of the graph and stick it into an already-marked region (hang