[CMake] Calling cmake from within cmake.

[Sylvain Benner]

>
> BTW you don't need the ARGS keyword in EXEC_PROGRAM,
> ADD_CUSTOM_COMMAND, or ADD_CUSTOM_TARGET.  It's correct but archaic.
>
>   
ARGS is not needed with EXECUTE_PROCESS, not EXEC_PROGRAM ; )

--Sylvain