Fix or silence binder build warnings on clang

Bug: 302724232
Test: mma
Change-Id: Ibd0dd5ef3c985901ab850cb0a589256efadb06a1
diff --git a/libs/binder/rust/tests/serialization.hpp b/libs/binder/rust/tests/serialization.hpp
index 0041608..9edcd6d 100644
--- a/libs/binder/rust/tests/serialization.hpp
+++ b/libs/binder/rust/tests/serialization.hpp
@@ -14,7 +14,10 @@
  * limitations under the License.
  */
 
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wpragma-once-outside-header"
 #pragma once
+#pragma clang diagnostic pop
 
 #include <binder/IBinder.h>