[CMake] include directories variable?

[Sylvain Benner]

> How do I get the INCLUDE_DIRECTORIES path?  I need to feed into into the
> search path for the swig command line.
>   
Documentation taken from a "man cmake" command:

GET_DIRECTORY_PROPERTY
       Get a property of the directory.

         GET_DIRECTORY_PROPERTY(VAR [DIRECTORY dir] property)

       Get a property from the Directory.  The value of the property is
       stored  in the variable VAR. If the property is not found, CMake
       will  report  an  error.  The  properties  include:   VARIABLES,
       CACHE_VARIABLES,    COMMANDS,    MACROS,    INCLUDE_DIRECTORIES,
       LINK_DIRECTORIES, DEFINITIONS, INCLUDE_REGULAR_EXPRESSION, LIST-
       FILE_STACK,  PARENT_DIRECTORY,  and  DEFINITION varname.  If the
       DIRECTORY argument is provided then the property of the provided
       directory  will  be  retrieved instead of the current directory.
       You can only get properties of a directory during  or  after  it
       has been traversed by cmake.

--Sylvain