enable ccache under Windows
BornAgain builds currently take <2' under Linux, 8' on a very modest Macbook, 16' under Windows. With several people developing in parallel, this is getting in the way of efficient test and review workflow.
To speed up compilation under Windows, we need to get ccache
to work. Currently, it's disabled or ineffective.
Probably this requires changing the CMake generator from VS to Ninja. Furthermore, Ninja needs to be parameterized such that it uses VS as compiler (and not mingw). See discussion in the bornagain Slack channel around 10mar21.
Solution of this issue should consist in a correction to the Windows Powershell script section in .gitlab-ci.yml. However, things should first be tried out on a local Windows machine.