hg: jdk/sandbox: 8212612: Add documentation about Arguments::_exit_hook

[chris.hegarty at oracle.com]

Changeset: c657b5b0e666
Author:    iklam
Date:      2018-10-17 21:51 -0700
URL:       http://hg.openjdk.java.net/jdk/sandbox/rev/c657b5b0e666

8212612: Add documentation about Arguments::_exit_hook
Reviewed-by: hseigel, dlong, dholmes

! src/hotspot/share/runtime/arguments.cpp
! src/hotspot/share/runtime/arguments.hpp
! src/java.base/share/native/include/jni.h