Implemented the Word64Popcnt TurboFan operator for x64.

src/compiler/mips64/instruction-selector-mips64.cc

Index: src/compiler/mips64/instruction-selector-mips64.cc
diff --git a/src/compiler/mips64/instruction-selector-mips64.cc b/src/compiler/mips64/instruction-selector-mips64.cc
index b0841790621b02f81e2588ea6aecbad831ffcbc4..bd42590d42001ff7f2c90a72c1939e6686cb5f06 100644
--- a/src/compiler/mips64/instruction-selector-mips64.cc
+++ b/src/compiler/mips64/instruction-selector-mips64.cc
@@ -330,6 +330,9 @@ void InstructionSelector::VisitWord64Ctz(Node* node) { UNREACHABLE(); }
 void InstructionSelector::VisitWord32Popcnt(Node* node) { UNREACHABLE(); }
 
 
+void InstructionSelector::VisitWord64Popcnt(Node* node) { UNREACHABLE(); }
+
+
 void InstructionSelector::VisitWord64Ror(Node* node) {
   VisitRRO(this, kMips64Dror, node);
 }