[MacPorts] #47197: cmake-based ports: add cmake.out_of_source yes/no

[René J.V. Bertin]

Talking about CMake: here's a very useful tidbit I just discovered:

https://blogs.kde.org/2011/11/11/cool-new-stuff-cmake-286-3-standard-way-disable-optional-packages

This might be useful enough to add a macro to the cmake PortGroup, for ports that need to disable several features (the cmake macro is quite long, a macro accepting a list of package names to disable (or (re)enable) might be more readable.

R