cmake ALLEGRO_HAVE_SCHED_YIELD examples

liballeg/allegro5 CMakeLists.txt :526 

check_function_exists(sched_yield ALLEGRO_HAVE_SCHED_YIELD)

adventuregamestudio/ags libsrc/allegro/CMakeLists.txt :52 

check_function_exists(sched_yield ALLEGRO_HAVE_SCHED_YIELD)