Backport of JEP 254 (Compact Strings) to OpenJDK 8

[John Platts]

I am interested in OpenJDK 8 builds with JEP 254 (Compact Strings) support 
backported from OpenJDK 9. I like the compact strings work that is being done 
in JDK 9, but I am interested in a OpenJDK 8 build with backported JEP 254 
support since I am working with Java applications that might not work in 
OpenJDK 9 yet and since I would like take advantage of the feature in a 
backported OpenJDK 8 build instead of having to wait for the JDK 9 release.