fn waitpid(pid: i32, flags: u32) u32 {
    const Status = if (builtin.link_libc) c_uint else u32;
    var status: Status = undefined;
    while (true) {
        var ret: c_int = system.waitpid(pid, &status, flags);
        if (ret == -1) {
            if (std.os.errno(ret) == 4) continue; //EINTR
            unreachable;
        }
        return @intCast(u32, ret);
    }
}