After doing the exact same thing on a Windows machine I was able to compare all Makefiles. I noticed that the main Makefile on OSX was lacking all Qt' modules (SUBTARGETS was empty). So I started to find out why this happend. After a while I noticed that the .gitmodules file was in a different location comparing to the Windows setup. After moving it into the src/ dir the make command finally started to work.
I'm not sure why it moved but maybe it is a bug in Keka so it doesn't handle dot prefixed files correctly.