Bug 1353181 followup - Fix non-DEBUG warnings-as-errors bustage.

xpcom/string/nsSubstring.cpp

@@ -194,7 +194,14 @@ nsStringBuffer::AddRef()
   // first increment on that thread.  The necessary memory
   // synchronization is done by the mechanism that transfers the
   // pointer between threads.
-  uint32_t count = mRefCount.fetch_add(1, std::memory_order_relaxed) + 1;
+#ifdef NS_BUILD_REFCNT_LOGGING
+  uint32_t count =
+#endif
+    mRefCount.fetch_add(1, std::memory_order_relaxed)
+#ifdef NS_BUILD_REFCNT_LOGGING
+    + 1
+#endif
+    ;
   STRING_STAT_INCREMENT(Share);
   NS_LOG_ADDREF(this, count, "nsStringBuffer", sizeof(*this));
 }