RFR: 8276546: [IR Framework] Whitelist and ignore CompileThreshold

[Christian Hagedorn]

This patch whitelists `CompileThreshold` and ignores it if passed as JTreg VM/Java option flag to a test. The reason to do this is that our CI executes `-XX:-TieredCompilation` in combination with `CompileThreshold` and therefore IR matching will not be performed (because `CompileThreshold` is not whitelisted). This patch changes this.

Setting `CompileThreshold` with `TestFramework::addFlags/runWithFlags()` will normally apply the flag.

Thanks,
Christian

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Commit messages:
 - 8276546: [IR Framework] Whitelist and ignore CompileThreshold

Changes: https://git.openjdk.java.net/jdk/pull/6312/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6312&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8276546
  Stats: 109 lines in 3 files changed: 106 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6312.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6312/head:pull/6312

PR: https://git.openjdk.java.net/jdk/pull/6312