RFR: 8245236: Remove MO_VOLATILE Access decorator

[Kim Barrett]

Please review this change with replaces uses of the MO_VOLATILE memory
order Access decorator with uses of the MO_RELAXED decorator.  Uses of
MO_VOLATILE generally assume non-word-tearing semantics, so a relaxed
atomic access is more appropriate.  As a result, we can eliminate the
MO_VOLATILE decorator.

CR:
https://bugs.openjdk.java.net/browse/JDK-8245236

Webrev:
https://cr.openjdk.java.net/~kbarrett/8245236/open.00/

Testing:
mach5 tier1.