QTest's signal dumper is not thread-safe and may assert

QTest's best feature (the signal dumper `-vs`) is a little broken.

In qtbase\src\testlib\qsignaldumper.cpp there're statics (iLevel, ignoreLevel). They are not synchronized and may be accessed from any thread. iLevel indicates the indentation and may turn negative if a thread reads a 0 before decrementing! It also creates a total mess of the output even if this variable is made atomic.

Should it be a thread_local? For a BlockingQueued emission it would logically make sense to keep the indentation level across threads.