RFR: Add preempt logging to find bug.

[Coleen Phillimore]

On Wed, 4 Aug 2021 21:30:44 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

> I made the logging product level and added the preempt tag for preemption, in order to find out why the Preempt.java test is failing a lot.  It seems to only be failing in the interpreter test cases.  Anyway, if performance is a concern with preemption, we can move this back to log_develop_trace.

Ron says looks good in slack.  Thanks!

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PR: https://git.openjdk.java.net/loom/pull/56