Add support for building OpenJDK on PPC64 (from the PowerPC/AIX Port - JEP175)

The PowerPC/AIX Port adds a JIT VM for PowerPC builds on both AIX and Linux OSes. I modified the script in order to add ppc64 arch checks and enable building OpenJDK on a PPC64 machine. 

Some other changes were:
- replace 'uname -p' calls by 'uname -m' (see [this example](https://www.mulesoft.org/jira/browse/MULE-1288) for why)
- add an EXTRA_FLAGS into openjdk8/build.sh since I needed to set the proper interpreter (let me know if there's a better way)

The JEP175 code lives on another repository for now, I didn't set that repo as the default in master to avoid conflicts - I set it as default on my [use-openjdk-powerpc-port](https://github.com/tdaitx/obuildfactory/tree/use-openjdk-powerpc-port).