RFR (XS): 8032634: Add #ifdef PPC64 around OrderAccess operations on _thread_state.

[Lindenmaier, Goetz]

Hi,

please review and test this small change:
http://cr.openjdk.java.net/~goetz/webrevs/8032634-1-ifdef/
Please also review it for jdk8u.

There are concerns that the OrderAccess operations we added to accesses of
_thead_state for ppc64 harm performance on other platforms.  Thus this change adds
guards #ifdef PPC64 around it.

Best regards,
  Goetz.