al_run_main - Allegro 5 API

       This  function  is useful in cases where you don’t have a main() function but want to run Allegro (mostly
       useful in a wrapper library).  Under Windows and Linux this is no problem because  you  simply  can  call
       al_install_system(3alleg5).     But    some    other    system    (like    OSX)   don’t   allow   calling
       al_install_system(3alleg5) in the main thread.  al_run_main will know what to do in that case.

       The passed argc and argv will simply be passed on to user_main and the return value of user_main will  be
       returned.

Allegro reference manual                                                                    al_run_main(3alleg5)

       al_run_main - Allegro 5 API

              #include <allegro5/allegro.h>

              int al_run_main(int argc, char **argv, int (*user_main)(int, char **))