RFR: 8165434: [JVMCI] remove uses of setAccessible

[Doug Simon]

JVMCI currently uses java.lang.reflect.AccessibleObject.setAccessible to get at private internals of certain JDK objects (e.g. java.lang.reflect.Method::slot). In light of changes around java.lang.reflect.AccessibleObject::setAccessible at http://openjdk.java.net/jeps/261, this may require extra command line options at some point. To avoid that, I’ve removed all uses of setAccessible in JVMCI.

http://cr.openjdk.java.net/~dnsimon/8165434/
https://bugs.openjdk.java.net/browse/JDK-8165434

-Doug