[arm][arm64] Improve CountTrailingZero implementation.

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

Index: src/compiler/mips/instruction-selector-mips.cc
diff --git a/src/compiler/mips/instruction-selector-mips.cc b/src/compiler/mips/instruction-selector-mips.cc
index 9a1867029b4c8d839422108ca568057dfb368bed..548b66765a21ee6d850d79a7f0bff7b41601908c 100644
--- a/src/compiler/mips/instruction-selector-mips.cc
+++ b/src/compiler/mips/instruction-selector-mips.cc
@@ -401,6 +401,9 @@ void InstructionSelector::VisitWord32Clz(Node* node) {
 }
 
 
+void InstructionSelector::VisitWord32ReverseBits(Node* node) { UNREACHABLE(); }
+
+
 void InstructionSelector::VisitWord32Ctz(Node* node) {
   MipsOperandGenerator g(this);
   Emit(kMipsCtz, g.DefineAsRegister(node), g.UseRegister(node->InputAt(0)));