Pass the default Python version (or the version required by port)
for CMake based ports. By default CMake picks up the highest
available version of Python package, therefore ports which use CMake
may fail to build or link to different Python library than one could
expect (e.g. bugs 199685, 200518).
In essence this commit reverts r366996.

PR: 168159
Exp-run by: antoine
Approved by: mva