Comment by pmr_

At first I thought "a build system which automatically figures out what to build and how to build it purely based on the source code" included figuring out library dependencies. It looks like I was wrong though and you still have to set linker and compiler flags yourself. I think actually understanding your dependencies (minimum versions, different build configurations and all) and handling them in a unified manner without too much special casing for the peculiarities. CMake already does this quite well, but there is still lots of room for improvement.