RFR: 8181085: Race condition in method resolution may produce spurious NullPointerException

[Andrew Haley]

Just to be clear on my position: we want to constrain the compiler as
little as we can, while maintaining correctness.  x86 OrderAccess was
incorrect, so compiler barriers had to be added.  Where volatile is
sufficient we should use that today, but bear in mind that racy
accesses are now undefined behaviour in C++.

Andrew.