[gcc] Fix -Wempty-body warning. NFC.

GitOrigin-RevId: d2acf229279233a6ff7317cc2268a65b7bc5fe80
diff --git a/include/atomic b/include/atomic
index f00f7b8..70f1769 100644
--- a/include/atomic
+++ b/include/atomic
@@ -1525,7 +1525,7 @@
         else if(__elapsed > chrono::microseconds(4))
             __libcpp_thread_yield();
         else
-            ; // poll
+            {} // poll
         return false;
     }
 };