Make v8 build with -Wimplicit-fallthrough in ppc and s390 configs.

R=joransiu@ca.ibm.com

Change-Id: I1377d90de81eb5f0ecfe9318c3126f55fb36cac2
Reviewed-on: https://chromium-review.googlesource.com/929753Reviewed-by: Joran Siu <joransiu@ca.ibm.com>
Commit-Queue: Junliang Yan <jyan@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#51451}

src/compiler/s390/code-generator-s390.cc

@@ -260,28 +260,28 @@ Condition FlagsConditionToCondition(FlagsCondition condition, ArchOpcode op) {
       // unsigned number never less than 0
       if (op == kS390_LoadAndTestWord32 || op == kS390_LoadAndTestWord64)
         return CC_NOP;
-    // fall through
+    V8_FALLTHROUGH;
     case kSignedLessThan:
       return lt;
     case kUnsignedGreaterThanOrEqual:
       // unsigned number always greater than or equal 0
       if (op == kS390_LoadAndTestWord32 || op == kS390_LoadAndTestWord64)
         return CC_ALWAYS;
-    // fall through
+    V8_FALLTHROUGH;
     case kSignedGreaterThanOrEqual:
       return ge;
     case kUnsignedLessThanOrEqual:
       // unsigned number never less than 0
       if (op == kS390_LoadAndTestWord32 || op == kS390_LoadAndTestWord64)
         return CC_EQ;
-    // fall through
+    V8_FALLTHROUGH;
     case kSignedLessThanOrEqual:
       return le;
     case kUnsignedGreaterThan:
       // unsigned number always greater than or equal 0
       if (op == kS390_LoadAndTestWord32 || op == kS390_LoadAndTestWord64)
         return ne;
-    // fall through
+    V8_FALLTHROUGH;
     case kSignedGreaterThan:
       return gt;
     case kOverflow:

src/ppc/disasm-ppc.cc

@@ -269,6 +269,7 @@ int Decoder::FormatOption(Instruction* instr, const char* format) {
             converter_.NameOfAddress(reinterpret_cast<byte*>(instr) + off));
         return 8;
       }
+      break;
       case 's': {
         DCHECK_EQ(format[1], 'h');
         int32_t value = 0;

src/ppc/simulator-ppc.cc

@@ -2155,8 +2155,8 @@ void Simulator::ExecuteGeneric(Instruction* instr) {
       }
       break;
     }
-    case STFSUX: {
-      case STFSX:
+    case STFSUX: V8_FALLTHROUGH;
+    case STFSX: {
       int frs = instr->RSValue();
       int ra = instr->RAValue();
       int rb = instr->RBValue();
@@ -2185,8 +2185,8 @@ void Simulator::ExecuteGeneric(Instruction* instr) {
       }
       break;
     }
-    case STFDUX: {
-      case STFDX:
+    case STFDUX: V8_FALLTHROUGH;
+    case STFDX: {
       int frs = instr->RSValue();
       int ra = instr->RAValue();
       int rb = instr->RBValue();
@@ -3214,8 +3214,8 @@ void Simulator::ExecuteGeneric(Instruction* instr) {
       break;
     }
 
-    case STFSU: {
-      case STFS:
+    case STFSU: V8_FALLTHROUGH;
+    case STFS: {
       int frs = instr->RSValue();
       int ra = instr->RAValue();
       int32_t offset = SIGN_EXT_IMM16(instr->Bits(15, 0));
@@ -3243,7 +3243,6 @@ void Simulator::ExecuteGeneric(Instruction* instr) {
       }
       break;
     }
-
     case STFDU:
     case STFD: {
       int frs = instr->RSValue();

src/s390/disasm-s390.cc

@@ -288,6 +288,7 @@ int Decoder::FormatOption(Instruction* instr, const char* format) {
             converter_.NameOfAddress(reinterpret_cast<byte*>(instr) + off));
         return 8;
       }
+      break;
       case 'm': {
         return FormatMask(instr, format);
       }