illumos gate

Issues found by gcc 7 build:

    pkginstall: this statement may fall through

    main.c:897:3: error: this statement may fall through [-Werror=implicit-fallthrough=]
       usage();
       ^~~~~~~
    main.c:899:2: note: here
      case 1: /* missing package instance */
      ^~~~
    main.c:901:3: error: this statement may fall through [-Werror=implicit-fallthrough=]
       usage();
       ^~~~~~~
    main.c:903:2: note: here
      case 2: /* just right! */
      ^~~~
    cc1: all warnings being treated as errors

    pkgremove: this statement may fall through

    main.c:1311:6: error: this statement may fall through [-Werror=implicit-fallthrough=]
       if (msg)
          ^
    main.c:1313:6: note: here
          case 10:
          ^~~~
    cc1: all warnings being treated as errors

    pkgadm: this statement may fall through

    lock.c: In function 'admin_lock':
    lock.c:398:4: error: this statement may fall through [-Werror=implicit-fallthrough=]
        log_msg(LOG_MSG_ERR, MSG_MISSING_OPERAND, optopt);
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    lock.c:400:3: note: here
       case '?':
       ^~~~
    cc1: all warnings being treated as errors