[CMake] Shared library for a executable

[Gonzalo]

I have the need to have a shared library be created and then this same 
library be accessed by my executable.
I want both to remain in different sibling directories and have one main 
CMakeList.txt that would call the other two CMakeList.txt (one in the 
lib dir, one in the exe dir) to build the library and the executable.
In addition, I would like my library to be able to be compiled by itself 
(its own project).

Can someone point me how to do this?  I set it up for my program with 
v2.8 but now this is failing on 3.4.2.

-- 
Gonzalo Garramuño
ggarra13 at gmail.com