Build Script Bugfix, master branch (2021.08.25.)

I made a big doo-doo in !46006 (merged). 😦 An excess -- token was left in the arguments given to the build tool, leading to a failure in building externals for any of the projects. 😦

This was reported in ATLINFR-4206, which this MR should fix.

I'm setting the full-build flag on the MR, just to make sure that all the scripts would run. But I think once the build of the main projects is underway, we may want to merge this in even before the CI would conclude. As CI jobs may start failing pretty soon as well. 😦

Pinging @elmsheus.