cmake ALLEGRO_HAVE_PROCFS_ARGCV examples

adventuregamestudio/ags libsrc/allegro/CMakeLists.txt :68

check_c_source_compiles("
        #include <sys/procfs.h>
        int main(void) {
            struct prpsinfo psinfo;
            psinfo.pr_argc = 0;
            return 0;
        }"
        ALLEGRO_HAVE_PROCFS_ARGCV
        )