Implemented the Word64Popcnt TurboFan operator for x64.

src/compiler/arm64/instruction-selector-arm64.cc

Index: src/compiler/arm64/instruction-selector-arm64.cc
diff --git a/src/compiler/arm64/instruction-selector-arm64.cc b/src/compiler/arm64/instruction-selector-arm64.cc
index 169c8e988dcbc8e7c146b6b0e7e5adc829d694e7..50ec74ba31d78fc1383a22dd340f2bed320fc58f 100644
--- a/src/compiler/arm64/instruction-selector-arm64.cc
+++ b/src/compiler/arm64/instruction-selector-arm64.cc
@@ -942,6 +942,9 @@ void InstructionSelector::VisitWord64Ctz(Node* node) { UNREACHABLE(); }
 void InstructionSelector::VisitWord32Popcnt(Node* node) { UNREACHABLE(); }
 
 
+void InstructionSelector::VisitWord64Popcnt(Node* node) { UNREACHABLE(); }
+
+
 void InstructionSelector::VisitInt32Add(Node* node) {
   Arm64OperandGenerator g(this);
   Int32BinopMatcher m(node);