8231202: Suppress warnings on non-serializable non-transient instance fields in serializable classes

Reviewed-by: rriggs, chegar

src/java.base/share/classes/java/util/Comparators.java

@@ -66,6 +66,7 @@ class Comparators {
         private static final long serialVersionUID = -7569533591570686392L;
         private final boolean nullFirst;
         // if null, non-null Ts are considered equal
+        @SuppressWarnings("serial") // Not statically typed as Serializable
         private final Comparator<T> real;
 
         @SuppressWarnings("unchecked")