QThread seems to leak QThreadData in some situations

Both tst_QSharedPointer and tst_QMutex have timing problems. When you run them sequentially on an unloaded machine, they pass and are asan-clean. If you run them on a loaded machine, however, such as as part of ctest -j24 on a 8C+HT = 16C machine, or just start the same test several times; then you get a sporadic memory leak of one of the QThreadData's reported, without corresponding leaks of their parent QThreadPrivate or QThread objects.. Logs for tst_QMutex and tst_QSharedPointer attached.

qthread.cpp:182 is

    if (!data)
        data = new QThreadData;  // L182

Line numbers are as at 53b6c88a2529a5767b2f4c6ff91680b93dc5e357.