bind span expression to avoid multiple evaluation

Author: haphungw

src/lro/src/internal/tracing.rs

@@ -97,10 +97,15 @@ macro_rules! record_polling_attributes {
         #[cfg(google_cloud_unstable_tracing)]
         {
             if let Ok(attempt) = $crate::POLL_ATTEMPT_COUNT.try_with(|c| *c) {
-                $span.record("gcp.longrunning.poll_attempt_count", attempt);
-                $span.record("gcp.longrunning.done", false);
+                let span = &$span;
+                span.record("gcp.longrunning.poll_attempt_count", attempt);
+                span.record("gcp.longrunning.done", false);
             }
         }
+        #[cfg(not(google_cloud_unstable_tracing))]
+        {
+            let _ = &$span;
+        }
     };
 }