Building OpenJDK libraries using IcedTea Project for JamVM

[Stefan Ring]

> FWIW, you should be able to create a snapshot zip from
> http://sourceforge.net/p/jamvm/code/, which contains an implementation
> of the missing function, and use IcedTea's --with-jamvm-src-zip
> switch.

This does not work. I managed to build it in a slightly hacky way now:

The snapshot file from sourceforge cannot be used directly. Despite it
being called src-zip, icedtea expects it to be a .tar.gz file. The
directory inside the tarball must have a name like "jamvm-*". I
created mine using this:

git archive --prefix=jamvm-2.0.0/ HEAD |gzip > ~/temp/jamvm.tgz

Unfortunately, when using this option, the sha256sum will still be
checked, so I just removed the entire if-block from the Makefile (look
for JAMVM_SHA256SUM).

$ ./openjdk.build/j2sdk-image/bin/java -version
java version "1.7.0_71"
IcedTea Runtime Environment (2.5.4pre01+rf7b45c531997) (CentOS build
1.7.0_71-b14)
JamVM (build 2.0.1-devel, inline-threaded interpreter)