RFR: JDK-8293344: JDK-8242181 broke stack printing for non-attached threads

[Thomas Stuefe]

https://bugs.openjdk.org/browse/JDK-8242181 gave us source infos in call stacks on Linux, which is really nice, but it made stack printing more vulnerable. We now require Thread::current, which makes stack printing fail and crash in non-attached threads. Causes truncated or missing stacks in hs-err file resp. crashes if stack printing is used outside error reporting.

I tested the fix manually.

I also am working on a testing facility for cases like these, which I will introduce in a separate RFE (see https://bugs.openjdk.org/browse/JDK-8293346).

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Commit messages:
 - JDK-8293344-stack-printing-nonattached-threads-broken

Changes: https://git.openjdk.org/jdk/pull/10158/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10158&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8293344
  Stats: 6 lines in 1 file changed: 3 ins; 2 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/10158.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10158/head:pull/10158

PR: https://git.openjdk.org/jdk/pull/10158