String concatenation fails with implicit toString() on package-private class

JCK build fails with new jdk9 builds that optimize string concatenation.
The use case is reduced to:

---- JTF_Slot.java ----
package p1;
public class JTF_Slot { public Hold cls_decl = new Hold();}
class Hold { public String toString() {return "passed"; }}

---- test.java ----
public class test {
    public static void main(String[] argv) {
        p1.JTF_Slot mainRoot = new p1.JTF_Slot();
        System.out.println(""+(mainRoot.cls_decl)+"");
    }
}

> java -version
java version "9-ea"
Java(TM) SE Runtime Environment (build 9-ea+108-2016-03-02-173138.javare.4571)
Java HotSpot(TM) 64-Bit Server VM (build 9-ea+108-2016-03-02-173138.javare.4571, mixed mode)

> javac -XDstringConcat=inline -cp . -d . JTF_Slot.java test.java ; java -cp . test
passed

> javac -cp . -d . JTF_Slot.java test.java ; java -cp . test
Exception in thread "main" java.lang.BootstrapMethodError: java.lang.IllegalAccessError: tried to access class p1.Hold from class test
at test.main(test.java:4)
Caused by: java.lang.IllegalAccessError: tried to access class p1.Hold from class test
... 1 more
> hostname
scaaa744