RFR: 8270447: [IR Framework] Add missing compilation level restriction when using FlipC1C2 stress option

[Christian Hagedorn]

On Thu, 22 Jul 2021 08:01:27 GMT, Christian Hagedorn <chagedorn at openjdk.org> wrote:

> A stress test with the IR framework option `FlipC1C2` for the newly converted Valhalla tests ([JDK-8263024](https://bugs.openjdk.java.net/browse/JDK-8263024)) resulted in invalid compilation requests (an exception is thrown) for unavailable compiler levels. A compilation level restriction after the flip from C1 -> C2 and vice versa was missing and also an exclusion when asserting on specific compilation levels with `DFlipC1C2`. I also included some small style fixes.
> 
> Thanks,
> Christian

Thanks Tobias for your review!

-------------

PR: https://git.openjdk.java.net/jdk/pull/4866