Decouple compile_all from compile_all_run_unittests_TG to reduce makespan

In order to reduce the makespan on Enterprise RHEL 62 (and possibly others), the proposal is to move compile_all into its own task group - thereby allowing it to be scheduled and executed independent of compile_all_run_unittests_TG. While this is less efficient from a processing perspective, it will allow us to start on the longest running tasks early and therefore reduce makespan. We can claw back some of this duplicate processing by also moving the unit test execution to compile_all - but that presents a larger experience change that will be capture in a future ticket.