[jdk25u] RFR: 8345810: Custom launchers must be linked with pthread to avoid dynamic linker issues

[Aleksey Shipilev]

Improves jpackage and test reliability, especially with older glibc-s that have `dlerror` issues under concurrent access.

Additional testing:
 - [x] Linux x86_64 server fastdebug, observing the failure with GCC 7.3.1
 - [x] Linux x86_64 server fastdebug, `sun/management/jmxremote`, 20x, no failures
 - [x] Linux x86_64 server fastdebug, `tools/jpackage`, 5x, no failures
 - [x] Linux x86_64 server fastdebug, `jdk_all`, no failures

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Commit messages:
 - Backport 685da0323b27abda5ab0484f4c8abaaeeff882ea

Changes: https://git.openjdk.org/jdk25u/pull/257/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk25u&pr=257&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8345810
  Stats: 3 lines in 2 files changed: 1 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk25u/pull/257.diff
  Fetch: git fetch https://git.openjdk.org/jdk25u.git pull/257/head:pull/257

PR: https://git.openjdk.org/jdk25u/pull/257