x86: never set i386_cpu_flags' "unused" field

Setting this field risks cpu_flags_all_zero() mistakenly returning
"false" when the object passed in was e.g. the result of ANDing together
two objects which had the bit set, or ANDNing together an object with
the field set and one with the field clear.

While there also avoid setting CpuNo64: Like Cpu64 this is driven
differently anyway and hence shouldn't be set anywhere by default.

Note that the moving of the two items in i386-gen.c's cpu_flags[] is
only for documentation purposes (and slight reducing of overhead), as
the fields are sorted anyway upon program start.

opcodes/i386-gen.c

@@ -628,8 +628,6 @@ static bitfield cpu_flags[] =
   BITFIELD (CpuPREFETCHWT1),
   BITFIELD (CpuSE1),
   BITFIELD (CpuCLWB),
-  BITFIELD (Cpu64),
-  BITFIELD (CpuNo64),
   BITFIELD (CpuMPX),
   BITFIELD (CpuAVX512IFMA),
   BITFIELD (CpuAVX512VBMI),
@@ -676,6 +674,8 @@ static bitfield cpu_flags[] =
   BITFIELD (CpuINVLPGB),
   BITFIELD (CpuTLBSYNC),
   BITFIELD (CpuSNP),
+  BITFIELD (Cpu64),
+  BITFIELD (CpuNo64),
 #ifdef CpuUnused
   BITFIELD (CpuUnused),
 #endif
@@ -1068,9 +1068,10 @@ process_i386_cpu_flag (FILE *table, char *flag, int macro,
       else
 	next = flag + 1;
 
-      /* First we turn on everything except for cpu64.  */
+      /* First we turn on everything except for cpu64, cpuno64, and - if
+         present - the padding field.  */
       for (i = 0; i < ARRAY_SIZE (flags); i++)
-	if (flags[i].position != Cpu64)
+	if (flags[i].position < Cpu64)
 	  flags[i].value = 1;
 
       /* Turn off selective bits.  */

opcodes/i386-init.h

@@ -25,7 +25,7 @@
       1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, \
       1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, \
       1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, \
-      1, 1, 0, 1, 1 } }
+      1, 1, 0, 0, 0 } }
 
 #define CPU_GENERIC32_FLAGS \
   { { 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, \

opcodes/i386-opc.h

@@ -272,6 +272,9 @@ enum
   CpuTLBSYNC,
   /* SNP instructions required */
   CpuSNP,
+
+  /* NOTE: These last three items need to remain last and in this order. */
+
   /* 64bit support required  */
   Cpu64,
   /* Not supported in the 64bit mode  */
@@ -417,6 +420,7 @@ typedef union i386_cpu_flags
       unsigned int cpuinvlpgb:1;
       unsigned int cputlbsync:1;
       unsigned int cpusnp:1;
+      /* NOTE: These last three fields need to remain last and in this order. */
       unsigned int cpu64:1;
       unsigned int cpuno64:1;
 #ifdef CpuUnused