Addition of a build system generator
I suggest to reuse a higher level build system than your current small make file so that powerful checks for software features will become easier.
The Makefile is already more complicated than I want it to be, actually. I'd like to get rid of the pkg-config stuff and just say -lpng if I could get away with it.
Are you interested in portable make files? How do you think about to improve software portability by feature checks?
No, I would in general like to depend only on facilities that exist on any reasonably modern Unix system.
There are some variations to consider for implementation details to be safe ...
As far as I know, everything I am doing is platform-neutral for the platforms I am targeting.
Does a tool like "autoscan" show any software dependencies that you find worth for further considerations?