RFR [14u]: 8241603: ZGC: java/lang/management/MemoryMXBean/MemoryTestZGC.sh crashes on macOS

[Langer, Christoph]

Hi,

please review the 14u backport of this ZGC fix for MacOS. We see the crash in 14, too.

Bug: https://bugs.openjdk.java.net/browse/JDK-8241603
Original Change: https://hg.openjdk.java.net/jdk/jdk/rev/f94239dfb99d
Webrev: http://cr.openjdk.java.net/~clanger/webrevs/8241603.14u/

The fix would apply cleanly but Atomic::fetch_and_add does not exist in 14. So I had to change:
processor_id = Atomic::fetch_and_add(&processor_id_next, 1) % os::processor_count();
to
processor_id = (Atomic::add(&processor_id_next, 1) - 1) % os::processor_count();

Thanks
Christoph