[8u20] backport 8042309: Some bugfixes for the ppc64 port.

[Vladimir Kozlov]

I am backporting these only ppc64 specific changes into 8u20. They are 
applied cleanly.

https://bugs.openjdk.java.net/browse/JDK-8042309
http://hg.openjdk.java.net/jdk9/hs-comp/hotspot/rev/b5e1deb7279e

Thanks,
Vladimir