RFR: 8364735: [asan] heap-use-after-free error detected in defaultStream::writer during VM shutdown

[David Holmes]

`ostream_exit` was deleting the stream underlying the `xtty` prior to nulling the `xtty` global variable, resulting in a use-after-free-error. Due to races during VM shutdown we cannot make use of `xtty` perfectly safe, but we can certainly narrow the window during which use-after-free is possible.

Testing:
 - tiers 1-3 sanity

Thanks

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Commit messages:
 - 8364735: [asan] heap-use-after-free error detected in defaultStream::writer during VM shutdown

Changes: https://git.openjdk.org/jdk/pull/26832/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26832&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8364735
  Stats: 6 lines in 1 file changed: 4 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/26832.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26832/head:pull/26832

PR: https://git.openjdk.org/jdk/pull/26832