Packaging libraries

So you have some code that is/was/should be a packaged as a library to isolate and encapsulate it... now it may have been directly compiled in a previous project, but now you need to isolate it.
First off, take careful examination of the code that was compiled in the previous project as it will most likely be benchmark for features. And if the new lib is not compiling the same set of files it will not be equivalent to the directly compiled code.