Is it possible to create a custom build system by compiling little bits at a time?

For example, you find the opengl code (or whatever gfx lib they're using), strip it down it only displays a window and doesn't reference any other gta code. Then it could be compiled without much trouble. Then another small system, say matrix transforms, can be isolated from the original code and integrated with the custom code to get it to compile.

This way you are creating your own build system ad hoc, and you find out what it needs as subsystems are added. Provided the code is decently decoupled and modular, it should be theoretically possible, even if it is still an absurd amount of work.

Or does this sound completely wacky to you?