versions override are not correctly taken into account with new CMake configuration

New CMake configuration of projects do not fix the versions of the dependencies (at most there's a constraint on the minimum version), so CMake, by default, picks up the first compatible version it finds, which might not be the one we want to use for the slot.

For example, a slot configured to build LHCb/master on the released Gaudi/v35r4 is not built correctly as it picks up Gaudi v36r0 (the latest release at the moment).