RFR: 8256569: Add C2 compiler stress flags to CTW

[Igor Ignatyev]

Hi all,

Could you please review this small patch which adds `-XX:+StressLCM`, `-XX:+StressGCM`, and `-XX:+StressIGVN` flags to the CTW test library? these flags have been found instrumental in increasing the probability to find C2 bugs. The patch also specifies `-XX:StressSeed` flag to keep CTW testing deterministic and reproducible.

testing:
* [x] `test/hotspot/jtreg/applications/ctw/modules/java_base.java` on `macos-x64`
* [x] `test/hotspot/jtreg/testlibrary_tests/ctw/` on `macos-x64`

Cheers,
-- Igor

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Commit messages:
 - 8256569: Add C2 compiler stress flags to CTW

Changes: https://git.openjdk.java.net/jdk/pull/1332/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1332&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8256569
  Stats: 8 lines in 1 file changed: 8 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1332.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1332/head:pull/1332

PR: https://git.openjdk.java.net/jdk/pull/1332