The current effective minimum required cmake version is 2.8.11 (as installed on CentOS7).
Strangely though CentOS6 comes with the newer cmake 2.8.12.
Having cmake 2.8.12 as minimum version on all targets would unblock
DM-4891 and enable upstream pybind11 cmake files to be used without modification.
This RFC proposes to provide cmake 2.8.12 in case the system version is too old.
We can do so either through conda or by other means if deemed better.