A number of companies will happily stand behind OpenJDK builds. I work for Pivotal, we build the JDKs and JREs that we ship to customers (and a lot of other languages too). Red Hat do too.
For comparsion, here's the repo where we keep our builder for OpenJDK: https://github.com/cloudfoundry/java-buildpack-dependency-bu...
I also found: https://github.com/ojdkbuild/ojdkbuild while looking for Red Hat's build scripts. I didn't find those, but only because I am bad at searching. They'll be published somewhere.