illumos gate

Issues found by gcc 7 build:

    ../../i86pc/os/trap.c:610:4: error: this statement may fall through [-Werror=implicit-fallthrough=]
        (void) die(type, rp, addr, cpuid);
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    ../../i86pc/os/trap.c:614:2: note: here
      case T_PGFLT:  /* system page fault */
      ^~~~

    ../../i86pc/os/trap.c: In function 'dump_ttrace':
    ../../i86pc/os/trap.c:2161:10: error: this statement may fall through [-Werror=implicit-fallthrough=]
          sys = &sysent[rec->ttr_sysnum];
          ~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~
    ../../i86pc/os/trap.c:2168:5: note: here
         case TT_SYSC:
         ^~~~

    ../../i86pc/boot/boot_console.c:507:3: error: this statement may fall through [-Werror=implicit-fallthrough=]
       ++p;
       ^~~
    ../../i86pc/boot/boot_console.c:508:2: note: here
      default:
      ^~~~~~~
    ../../i86pc/boot/boot_console.c:525:3: error: this statement may fall through [-Werror=implicit-fallthrough=]
       ++p;
       ^~~
    ../../i86pc/boot/boot_console.c:526:2: note: here
      default:
      ^~~~~~~

    ../../common/disp/cmt.c: In function 'pg_cmt_lineage_validate':
    ../../common/disp/cmt.c:1887:6: error: this statement may fall through [-Werror=implicit-fallthrough=]
       if (((pghw_t *)pg)->pghw_hw == PGHW_CHIP) {
          ^
    ../../common/disp/cmt.c:1894:2: note: here
      case CMT_LINEAGE_NON_PROMOTABLE:
      ^~~~

    ../../common/os/lgrp.c:3726:6: error: this statement may fall through [-Werror=implicit-fallthrough=]
       if (lgrp != lgrp_root) {
          ^
    ../../common/os/lgrp.c:3735:2: note: here
      case LGRP_MEM_POLICY_RANDOM:
      ^~~~
    ../../common/os/lgrp.c:3785:8: error: this statement may fall through [-Werror=implicit-fallthrough=]
       stat = LGRP_NUM_RANDOM_PROC;
       ~~~~~^~~~~~~~~~~~~~~~~~~~~~
    ../../common/os/lgrp.c:3788:2: note: here
      case LGRP_MEM_POLICY_RANDOM_PSET:
      ^~~~

    ../../common/os/lgrp.c:3726:6: error: this statement may fall through [-Werr
or=implicit-fallthrough=]
       if (lgrp != lgrp_root) {
      ^~~~

    ../../common/os/lgrp.c:3726:6: error: this statement may fall through [-Werr
or=implicit-fallthrough=]
       if (lgrp != lgrp_root) {
          ^
    ../../common/os/lgrp.c:3735:2: note: here
      case LGRP_MEM_POLICY_RANDOM:
      ^~~~
    ../../common/os/lgrp.c:3785:8: error: this statement may fall through [-Werr
or=implicit-fallthrough=]
       stat = LGRP_NUM_RANDOM_PROC;
       ~~~~~^~~~~~~~~~~~~~~~~~~~~~
    ../../common/os/lgrp.c:3788:2: note: here
      case LGRP_MEM_POLICY_RANDOM_PSET:
      ^~~~

    cc1: all warnings being treated as errors