One of my pet-peeves with C projects is that it's so often more or less "works on my machine" when written by Linux users (as a Windows and FreeBSD user it often hits you on both those platforms).
The article highlights a typical piece:
#if !(defined __GNUC__ || defined __clang__ || defined __TINYC__)
# define __attribute__(xyz) /* Ignore */
#endif
There is no reason that !defined check to not include a check for __attribute__ already being defined (a custom compiler author could then force an define for __attribute__ that translates to an internal __mycompiler__attribute__ replacement by default).
But outside of that, just trying to compile on FreeBSD you often run into systemd dependencies or other non-posix behaviors (Not to mention on Windows but I'm not here to bring on flamewars so I'll leave that part).
