REQUIRED keyword from all
find_package(...) calls that look for "externals".
This is meant to make our builds more robust against build errors. For instance in the recent dev3/dev4 nightlies ROOT was missing. Which stopped the builds completely. In fact, it is still missing in this nightly:
And while it's true that without a major external like ROOT not a whole lot from our projects will build successfully, the build should at least be attempted even in that case.