8280534: Enable compile-time doclint reference checking

Reviewed-by: serb, naoto, mchung, lancea, iris

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

@@ -73,6 +73,7 @@ package java.util;
  * {@link java.util.concurrent.Flow} API.
  */
 @Deprecated(since="9")
+@SuppressWarnings("doclint:reference") // cross-module links
 public class Observable {
     private boolean changed = false;
     private Vector<Observer> obs;

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

@@ -1647,6 +1647,7 @@ public final class ServiceLoader<S>
      * @revised 9
      */
     @CallerSensitive
+    @SuppressWarnings("doclint:reference") // cross-module links
     public static <S> ServiceLoader<S> load(Class<S> service,
                                             ClassLoader loader)
     {