gtest is built with the build-jdk

The build-jdk is a JDK built on the current sources that can execute on the build platform. This is needed when cross-compiling, in addition to the boot-jdk (which runs on the build platform, but is an older version of the JDK), and is different from the JDK resulting from the build (which can only execute on the target platform).

If we do not supply a pre-built build-jdk, the build system creates a new, on the fly, before starting the compilation proper.

This build-jdk includes gtest for hotspot, if available. This is just a waste of resources (and actually triggered a bug; which is how it was discovered).