[CMake] Calling cmake from within cmake.

[Josef Karthauser]

I want to recursively call cmake from a cmakelists.txt file to create
build directories for other projects.  I'm sure I saw something in the
docs that suggested a neat way of doing it that didn't involve executing
cmake explicitly as an external command, but I can't find it now I look
again.  Can anyone tell me what it is off the top of their heads please?

Ta,
Joe