RFR: 8297657: name demangling intermittently fails

[Fredrik Bredberg]

Fixes an intermittent name demangling problem (due to the uninitialized AbstractDecoder::_decoder_status field).
The problem affected hs-err stack traces on macosx-aarch64 and macosx-amd64.

I've done manual testing to verify the problem and the solution.
Also run tier1-5 after the fix without seeing any new problems.

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Commit messages:
 - 8297657: name demangling intermittently fails

Changes: https://git.openjdk.org/jdk/pull/13883/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13883&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8297657
  Stats: 6 lines in 1 file changed: 2 ins; 2 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/13883.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13883/head:pull/13883

PR: https://git.openjdk.org/jdk/pull/13883