Hi Nicolas,
Right you are :) Interesting cause, took me a while to figure out since Gui-Sdl builds just fine.. It seems another utils.h is picked up during compilation of utils.c instead - renaming the one in src/includes and changing the corresponding include in utils.c works fine - it's what then includes SDL_types.h -> SDL_stdinc.h.
Unfortunately I've then spent hours trying to understand why CMake find_package, or find_library for that matter, has no problem detecting my SDL install yet ld refuses to link it - complaining the framework cannot be found. Any resident Mac compiler feel free to chime in - I believe last time I compiled Hatari it was without SDL support although I'm not sure. I've tried forcing directories to no avail.