RFR: JDK-8272703: StressSeed should be set via FLAG_SET_ERGO

[Tobias Holenstein]

Set the `StressSeed` (added by JDK-8252219) via `FLAG_SET_ERGO` if the seed is generated by the VM (i.e., not set via the command line). This way, `StressSeed` will be added to the "[Global flags]" section of the hs_err file on crash and can be used to reproduce the issue.

If `RepeatCompilation` is on and no `StressSeed` is set, a new `StressSeed` is generated for every compilation. The reason for this is that some Bugs are only triggered intermittent, because they depend on the `StressSeed`.

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Commit messages:
 - JDK-8272703: RepeatCompilation check added
 - JDK-8272703: RepeatCompilation
 - JDK-8272703: StressSeed should be set via FLAG_SET_ERGO

Changes: https://git.openjdk.java.net/jdk/pull/5599/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5599&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8272703
  Stats: 6 lines in 1 file changed: 4 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5599.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5599/head:pull/5599

PR: https://git.openjdk.java.net/jdk/pull/5599