The authors wrote to say that a student on the paper

"set up a temporary github account for potential public source code
release a long time ago, but later we decided not to release the code
since it's being tech transferred to industry. The code at github is
thus very incomplete (and no wonder it does not build) and we have
never publicly advertised the link."

(The code was found by a crawler and associated with their paper.)

The authors assert that they cannot release the source for this
project due to restrictions put on them by their industrial
sponsors. (Other projects by the lead author do indeed publish
source.)

The unavailability of the source means that this paper is outside the
scope of the original Collberg, et al. study.