RFR 8232010: Shenandoah: implement self-fixing native barrier

[Zhengyu Gu]

Please review this patch that implements self-fixing LRB for in native oops.

Bug: https://bugs.openjdk.java.net/browse/JDK-8232010
Webrev: http://cr.openjdk.java.net/~zgu/JDK-8232010/webrev.00/

Test:
   hotspot_gc_shenandoah (fastdebug and release) with x86_32 and x86_64 
JVM on Linux.

Thanks,

-Zhengyu