Java 17 compilation fails when running on Java 11

[aumann]

Following the discussion linked below:

My intuition would have been that BREE, Manifest JavaSE-17 and setting the execution environment in the target platform to JavaSE-17 is enough. However, as soon as we use actual additions from the 17 runtime library (like List.toStream()) the compiler starts complaining. The compile errors vanish as soon as tycho itself runs on a JDK 17.

Maybe my expectations are just wrong? Otherwise, I'd open an issue.

Versions: 2.6.0, 2.7.1 and 2.7.2

I will open a draft pull request containing the test project inside tycho-it

Originally posted by @aumann in https://github.com/eclipse/tycho/discussions/938