Installing a program can be a difficult thing. We all need help with this sometime. The first thing you usually do is download the source archive . There are quite some hints in the Download FAQ .
Comments are quite good - but scrolling around, and editing can be tricky.
The defaults come from configure. But this is a special case, of course. See the full log for details. When installing Vim for another system then this cache file has to be deleted first. Now please check the pathnames in the Makefile and the user configuration section in config.h.