CTZ instruction implemented as optional operator.

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

Index: src/compiler/arm/instruction-selector-arm.cc
diff --git a/src/compiler/arm/instruction-selector-arm.cc b/src/compiler/arm/instruction-selector-arm.cc
index f58a29de8a6410059ae1a2dec7bab80a407f7c1b..07b27afce93594e4c143f0978e01bbc35cf66c22 100644
--- a/src/compiler/arm/instruction-selector-arm.cc
+++ b/src/compiler/arm/instruction-selector-arm.cc
@@ -697,6 +697,9 @@ void InstructionSelector::VisitWord32Clz(Node* node) {
 }
 
 
+void InstructionSelector::VisitWord32Ctz(Node* node) { UNREACHABLE(); }
+
+
 void InstructionSelector::VisitInt32Add(Node* node) {
   ArmOperandGenerator g(this);
   Int32BinopMatcher m(node);