Just a reminder to all involved in this discussion, the work with cmake has one goal, which is to remove our dependency on rbuild and the maintenance load that using it entails.  rbuild has a lot of issues by itself, irrespective of the problems it causes in combination with the directory hierarchy, but trying to go to cmake isn't designed to solve those problems, just the ones rbuild itself causes.  It may ultimately make solving the combined issues easier, but that's a secondary, albeit important, consideration.  That restructuring of the directories will likely be necessary has very little to do with the cmake effort itself.  So let's not conflate the two issues.