[CMake] Compiling zlib and libpng with one command

[Hugh Sorby]

I am trying to compile zlib and libpng with one command, or more 
specifically one series of commands.  My aim is to get as simple as 
possible to the following

cmake
make
make install

So what I have done so far is to layout my directories like so:

third_party
|
--zlib
|
--libpng


In each directory I have a CMakeLists.txt file that will build the 
libraries.  So far so good.  Now with a clean system i.e. one where 
libpng can't find zlib (because it hasn't been built yet) I try executing:

cmake

Which runs as expected right up until libpng requires the existence of 
zlib.  So my problem is how to tell libpng that zlib is on it's way if 
it could only be a little patient.  Preferebly without having to touch 
the CMakeLists.txt file inside libpng directory

Also is this strategy likely to fly or is it never going to get off the 
ground?

Chreers.

Also, can CMake apply patches?