[arm][arm64] Improve CountTrailingZero implementation.

src/compiler/x64/instruction-selector-x64.cc

Index: src/compiler/x64/instruction-selector-x64.cc
diff --git a/src/compiler/x64/instruction-selector-x64.cc b/src/compiler/x64/instruction-selector-x64.cc
index 96f8e32f8d607d7f95692bbeb4615137261da3a6..b540aa9bb18c192565d84fed9c96ae853398da4e 100644
--- a/src/compiler/x64/instruction-selector-x64.cc
+++ b/src/compiler/x64/instruction-selector-x64.cc
@@ -622,6 +622,12 @@ void InstructionSelector::VisitWord32Ctz(Node* node) {
 }
 
 
+void InstructionSelector::VisitWord32ReverseBits(Node* node) { UNREACHABLE(); }
+
+
+void InstructionSelector::VisitWord64ReverseBits(Node* node) { UNREACHABLE(); }
+
+
 void InstructionSelector::VisitWord32Popcnt(Node* node) {
   X64OperandGenerator g(this);
   Emit(kX64Popcnt32, g.DefineAsRegister(node), g.Use(node->InputAt(0)));