Unfortunately, the external zip tool we use from the build system does not allow full control over time stamps (or possibly other metadata) in the zip file, which leads to zip files not being reproducible, but diffing in a handful of bytes.

I believe we can write our own zip tool in Java, and use that instead, to fully control the output and ensure it is reproducible. The trick is likely to do as in JDK-8327466 and utilize the functionality from JDK-8075526 (see https://mail.openjdk.org/pipermail/core-libs-dev/2015-June/034426.html).