RFR: JDK-8302595: use-after-free related to GraphKit::clone_map [v2]

[Justin King]

> `GraphKit::clone_map` duplicates `SafePointNode` and calls `Compile::record_for_igvn`. In some cases `SafePointNode` is not used so `Node::destruct` is called to cleanup. The `Unique_Node_List` returned by `Compile::for_igvn` still references the node which resides in freed memory which may or may not have been reused. We additionally need to remove the node from `Unique_Node_List` as well to prevent this from happening.
> 
> I introduced `GraphKit::destruct_map_clone` which undoes `GraphKit::clone_map`. It even clears the type, though I am not sure if this is necessary so feel free to suggest otherwise. Additionally it calls `delete` on `JVMState`, which is a noop, but it seems like the correct thing to do in case its ever changed.

Justin King has updated the pull request incrementally with one additional commit since the last revision:

  Update based on review
  
  Signed-off-by: Justin King <jcking at google.com>

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12578/files
  - new: https://git.openjdk.org/jdk/pull/12578/files/3ba792da..93e1b69d

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12578&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12578&range=00-01

  Stats: 12 lines in 3 files changed: 0 ins; 0 del; 12 mod
  Patch: https://git.openjdk.org/jdk/pull/12578.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12578/head:pull/12578

PR: https://git.openjdk.org/jdk/pull/12578