build's "scala" build system is ant-based and isn't really worth updating to use sbt, because there's no need anymore to "address the case in which a cycle exists between the core (library/compiler) and the modules" within dbuild — we can just let scripts/jobs/validate/publish-core do it for us and consume the artifacts it produces

once this is done, scala/scala#5311 can be merged, bye forever Ant!