RFR: CODETOOLS-7902951: jcstress: Optimize JNA loading paths

[Aleksey Shipilev]

Forked VMs unpack JNA libraries on every invocation. Those should actually be unpacked once by host VM, and then reused by forked VMs.

This saves about 30 ms per forked VM invocation.

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Commit messages:
 - Trying to save JNA libraries between forks

Changes: https://git.openjdk.java.net/jcstress/pull/59/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jcstress&pr=59&range=00
  Issue: https://bugs.openjdk.java.net/browse/CODETOOLS-7902951
  Stats: 73 lines in 4 files changed: 49 ins; 14 del; 10 mod
  Patch: https://git.openjdk.java.net/jcstress/pull/59.diff
  Fetch: git fetch https://git.openjdk.java.net/jcstress pull/59/head:pull/59

PR: https://git.openjdk.java.net/jcstress/pull/59