Fix #4143: Ignore lines "Picked up _JAVA_OPTIONS" in tests

[nicolasstucki]

No description provided.

[liufengyun]

LGTM

[allanrenucci]

I propose an alternative solution: discard any output generated before the program start running.

The way I would do this:

1. Add a String MessageStart to ChildJVMMain
2. Prints MessageStart before running the main at https://github.com/lampepfl/dotty/blob/1fdb94bfaac72fc7ef91bff058a902e2ea4b3f0f/compiler/test/dotty/tools/vulpix/ChildJVMMain.java#L26
3. Discard all lines before MessageStart at https://github.com/lampepfl/dotty/blob/1fdb94bfaac72fc7ef91bff058a902e2ea4b3f0f/compiler/test/dotty/tools/vulpix/RunnerOrchestration.scala#L121

If JVM logging is done within the call to meth.invoke(null, args), this will not work though

[nicolasstucki]

That sounds a lot more complex than required for this particular exceptional behavior.

[allanrenucci]

True, it is a bit more complex. But as you said, the current solution only fixes a particular exceptional behavior. What I propose should discard any logging done by the VM before the program execution. We don't want to add more special case fixes if it happens that the VM produces more logs in some other exceptional cases

[nicolasstucki]

Changes done