Hm... what does this command return? pkg-config --cflags sdl2 SDL2_image SDL2_mixer
This command is used by the makefile, and it generates the -I flag. If it's returning something incorrect, that would be causing the problem. (I imagine make install would have put your installation into /usr/local.)
If that's the problem, you can replace this command in the makefile with the correct -I command.
Another thought: you need the SDL2 header files. Does the configure && make && make install procedure install these, or does it just install the library itself?
