Simple differences - Missing APIs

Platforms often have missing APIs

Perhaps the most common difference

Some random examples from OpenSSH:

      arc4random        getopt             prctl             setresuid
      b64_ntop          getpeereid         pstat             setsid
      b64_pton          _getpty            readpassphrase    setvbuf
      bcopy             getrlimit          realpath          sigaction
      bindresvport_sa   getttyent          recvmsg           snprintf
      clock             glob               rresvport_af      socketpair
      closefrom         inet_aton          sendmsg           strerror
      dirfd             inet_ntoa          setdtablesize     strlcat
      fchmod            inet_ntop          setegid           strlcpy
      fchown            innetgr            setenv            strmode
      freeaddrinfo      login_getcapbool   seteuid           strnvis
      futimes           md5_crypt          setgroups         strtonum
      getaddrinfo       memmove            setlogin          strtoll
      getcwd            mkdtemp            setpcred          strtoul
      getgrouplist      openlog_r          setproctitle      sysconf
      getnameinfo       openpty            setrlimit         tcgetpgrp
