[CMake] Get program output in a variable?

[Zachary Pincus]

Hi guys,

I'm trying to make a better CMake script to find the presence of the  
Numerical Python libraries and their include directories. The easiest  
way to do this in some cases (e.g. with the newest version of said  
libraries, now called numpy) is to query the module itself within  
python.

Is there a good way within CMake to run a program? TRY_RUN seems to  
want to compile a file first... I'd just like to run something like:
"${PYTHON_EXECUTABLE} -c 'import numpy; print numpy.get_module_include 
()'"
and get the output in a CMake variable.

Is this possible? If so, something similar might be a better way of  
finding things like the python include path and so forth, rather than  
looking in hard-coded places in a FindPythonLibs.cmake file.

Zach