Fix ARM64 port after r22876.

src/compiler/linkage.cc

Index: src/compiler/linkage.cc
diff --git a/src/compiler/linkage.cc b/src/compiler/linkage.cc
index ce88a0695699a212ab0aa8234d55195114b8f7cf..466f65c8ba8397552c82e7da14c648ab811847d5 100644
--- a/src/compiler/linkage.cc
+++ b/src/compiler/linkage.cc
@@ -105,7 +105,7 @@ CallDescriptor* Linkage::GetRuntimeCallDescriptor(
 //==============================================================================
 // Provide unimplemented methods on unsupported architectures, to at least link.
 //==============================================================================
-#if !V8_TURBOFAN_TARGET
+#if !V8_TURBOFAN_BACKEND
 CallDescriptor* Linkage::GetJSCallDescriptor(int parameter_count, Zone* zone) {
   UNIMPLEMENTED();
   return NULL;
@@ -134,7 +134,7 @@ CallDescriptor* Linkage::GetSimplifiedCDescriptor(
   UNIMPLEMENTED();
   return NULL;
 }
-#endif  // !V8_TURBOFAN_TARGET
+#endif  // !V8_TURBOFAN_BACKEND
 }
 }
 }  // namespace v8::internal::compiler