Using -### is insufficient to discover the entire set of frontend jobs
needed to satisfy a given incremental compilation session because of the
presence of additional waves of recompilation. More concretely, any
additional compilation jobs whose queueing behavior depends on the set
of jobs reported by -### are, by definition, hidden from -###.
Note that it is also *not* possible to run the incremental build to
a fixpoint by iteratively executing said frontend jobs and re-running
the driver with -### because the build record is never updated to
account for the jobs executed by an external system.
Aimed at people writing build systems who won't be satisfied with
"just use xcodebuild" or "just use SwiftPM", mostly because they'll
go ahead doing what they're doing anyway and it'll be incorrect.
