Implemented the ctz Turbo Fan operator for x64.

src/x64/assembler-x64.cc

Index: src/x64/assembler-x64.cc
diff --git a/src/x64/assembler-x64.cc b/src/x64/assembler-x64.cc
index 0c5ba9dd06ea5ea9beff7e7cb550f6bbaad930be..81059ec80f0ea7ca76827a7cc2d954e195e6971d 100644
--- a/src/x64/assembler-x64.cc
+++ b/src/x64/assembler-x64.cc
@@ -781,6 +781,24 @@ void Assembler::bsfl(Register dst, const Operand& src) {
 }
 
 
+void Assembler::bsfq(Register dst, Register src) {
+  EnsureSpace ensure_space(this);
+  emit_rex_64(dst, src);
+  emit(0x0F);
+  emit(0xBC);
+  emit_modrm(dst, src);
+}
+
+
+void Assembler::bsfq(Register dst, const Operand& src) {
+  EnsureSpace ensure_space(this);
+  emit_rex_64(dst, src);
+  emit(0x0F);
+  emit(0xBC);
+  emit_operand(dst, src);
+}
+
+
 void Assembler::call(Label* L) {
   positions_recorder()->WriteRecordedPositions();
   EnsureSpace ensure_space(this);