[IR Framework] Whitelist and ignore CompileThreshold

Adapted description from: https://github.com/openjdk/jdk/pull/5903#issuecomment-957443870

Our CI currently only runs -XX:-TieredCompilation in combination with CompileThreshold which is not whitelisted. This means that IR matching is not performed in that case. That's the reason why we have not detected JDK-8275086 in our testing. I think the IR framework should be improved to just ignore any CompileThreshold flag settings and allow IR matching to be performed with -XX:-TieredCompilation in our CI.