RFR(xs): 8176442: [aix] assert(_thr_current == 0L) failed: Thread::current already initialized

[Thomas Stüfe]

Please review this small AIX change.

Issue: https://bugs.openjdk.java.net/browse/JDK-8176442
webrev:
http://cr.openjdk.java.net/~stuefe/webrevs/8176442-switch-off-compiler-level-tls-on-aix/webrev.00/webrev/


This change switches the implementation of Thread::current() from compiler
level TLS back to pthread library TLS. We see errors on AIX 5.3 machines
where compiler level TLS seems not to work correctly - new TLS variable
instances are sporadically left uninitialized.

For more details, please see the description and comments in the bug report.

Thank you, Thomas