Fix compilation on x64 architectures

src/x64/lithium-x64.h

Index: src/x64/lithium-x64.h
diff --git a/src/x64/lithium-x64.h b/src/x64/lithium-x64.h
index 0aab4431e3532ce041e5c52bcf09ec4b819a4bc0..49208f168b3e8b752769b2a7587be867cd648721 100644
--- a/src/x64/lithium-x64.h
+++ b/src/x64/lithium-x64.h
@@ -1791,8 +1791,7 @@ class LCallWithDescriptor V8_FINAL : public LTemplateResultInstruction<1> {
   LCallWithDescriptor(const CallInterfaceDescriptor* descriptor,
                       ZoneList<LOperand*>& operands,
                       Zone* zone)
-    : descriptor_(descriptor),
-      inputs_(descriptor->environment_length() + 1, zone) {
+    : inputs_(descriptor->environment_length() + 1, zone) {
     ASSERT(descriptor->environment_length() + 1 == operands.length());
     inputs_.AddAll(operands, zone);
   }
@@ -1807,7 +1806,6 @@ class LCallWithDescriptor V8_FINAL : public LTemplateResultInstruction<1> {
 
   int arity() const { return hydrogen()->argument_count() - 1; }
 
-  const CallInterfaceDescriptor* descriptor_;
   ZoneList<LOperand*> inputs_;
 
   // Iterator support.