Add tzcnt as an acceptable instruction to the x86-32 validator (it already

src/trusted/validator/x86/ncval_seg_sfi/gen/ncdisasmtab_64.h

 /* native_client/src/trusted/validator/x86/ncval_seg_sfi/gen/ncdisasmtab_64.h
  * THIS FILE IS AUTO-GENERATED. DO NOT EDIT.
  * Compiled for x86-64 bit mode.
  *
  * You must include ncdecode.h before this file.
  */
 
 static const char *kDisasmModRMOp[][kNaClMRMGroupsRange] = {
    {  /* 0 0 */  "undefined",
   /* 0 1 */  "undefined",
@@ skipping 1399 matching lines @@
   /* b2 */  "undefined",
   /* b3 */  "undefined",
   /* b4 */  "undefined",
   /* b5 */  "undefined",
   /* b6 */  "undefined",
   /* b7 */  "undefined",
   /* b8 */  "popcnt",
   /* b9 */  "reserved",
   /* ba */  "reserved",
   /* bb */  "reserved",
-  /* bc */  "reserved",
+  /* bc */  "tzcnt $Gv, $Ev",
   /* bd */  "lzcnt $Gv, $Ev",
   /* be */  "reserved",
   /* bf */  "reserved",
   /* c0 */  "undefined",
   /* c1 */  "undefined",
   /* c2 */  "cmpss $V, $W, $I",
   /* c3 */  "invalid",
   /* c4 */  "invalid",
   /* c5 */  "invalid",
   /* c6 */  "invalid",
@@ skipping 3679 matching lines @@
   /* f8 */  "invalid",
   /* f9 */  "invalid",
   /* fa */  "invalid",
   /* fb */  "invalid",
   /* fc */  "invalid",
   /* fd */  "invalid",
   /* fe */  "invalid",
   /* ff */  "invalid",
 };