RFR: 8303089: [jittester] Add time limit to IRTree generation

[Evgeny Nikitin]

Sometimes, the generation could take more than an hour and probably never stop. This PR adds a time limit (defaults to 10 minutes) to the generation of a single test.

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Commit messages:
 - 8303089: [jittester] Add time limit to IRTree generation

Changes: https://git.openjdk.org/jdk/pull/12722/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12722&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8303089
  Stats: 67 lines in 3 files changed: 40 ins; 6 del; 21 mod
  Patch: https://git.openjdk.org/jdk/pull/12722.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12722/head:pull/12722

PR: https://git.openjdk.org/jdk/pull/12722