[CMake] configuration input to cmake

[Jun Sun]

My build process involves a configuration stage. It roughly looks like
this:

* Generate cmakefile.inc and config.h from .config file
* Use cmake to generate solution files or makefiles
* Build with native toolchain

It is not clear to me whether I should use an external script to do 
step 1 or I can even do the first step with cmake itself.

I am very new to cmake. Sorry if this is a dumb question. :)

Cheers.

Jun