RFR: 8079315: UseCondCardMark broken in conjunction with CMS precleaning

[Andrew Haley]

Have we come to a complete standstill?

We have a number of AArch64 patches, needed for correctness, which are
blocked on this.  But part of the simple AArch64 fix, which would be a
StoreLoad barrier, requires a change to shared code.  I could submit
something #ifdef AARCH64, which probably wouldn't be popular.

Andrew.