[jdk8u-ri] RFR: 8201793: (ref) Reference object should not support cloning

[Poonam Bajaj]

This changeset backports the fix for 8201793 to jdk8u-ri.

With this change, `java.lang.ref.Reference::clone` method always throws `CloneNotSupportedException`.

-------------

Commit messages:
 - 8201793: (ref) Reference object should not support cloning

Changes: https://git.openjdk.java.net/jdk8u-ri/pull/6/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk8u-ri&pr=6&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8201793
  Stats: 118 lines in 2 files changed: 118 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk8u-ri/pull/6.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk8u-ri pull/6/head:pull/6

PR: https://git.openjdk.java.net/jdk8u-ri/pull/6