cmake ALLEGRO_HAVE_SYSCONF examples

liballeg/allegro5 CMakeLists.txt :527

check_function_exists(sysconf ALLEGRO_HAVE_SYSCONF)

adventuregamestudio/ags libsrc/allegro/CMakeLists.txt :56

check_function_exists(sysconf ALLEGRO_HAVE_SYSCONF)