8231630: Optimize boot loader with no bootclasspath append entry.
Summary: Optimize SystemDictionary::load_instance_class for boot loader. Immediately return NULL if the requested class is either in the unnamed package or unnamed module, or in a module not defined to the boot loader, when there is no bootclasspath append entry.
Reviewed-by: martin, aeubanks, dthomson, redestad, lfoltan, iklam
Welcome to the JDK!
===================
For information about building the JDK, including how to retrieve all
of the source code, please see either of these files:
* doc/building.html (html version)
* doc/building.md (markdown version)
See http://openjdk.java.net/ for more information about the OpenJDK
Community and the JDK.