8210721: Replace legacy serial exception field with Throwable::cause

Reviewed-by: dfuchs, lancea

src/java.base/share/classes/java/lang/System.java

@@ -2201,6 +2201,9 @@ public final class System {
                 return StringCoding.getBytesUTF8NoRepl(s);
             }
 
+            public void setCause(Throwable t, Throwable cause) {
+                t.setCause(cause);
+            }
         });
     }
 }