Extend TF test coverage to unsupported targets.

src/compiler/arm64/linkage-arm64.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #include "src/assembler.h"
 #include "src/code-stubs.h"
 #include "src/compiler/linkage.h"
 #include "src/compiler/linkage-impl.h"
 #include "src/zone.h"
 
 namespace v8 {
 namespace internal {
 namespace compiler {
 
+#if V8_TURBOFAN_TARGET
+
 struct LinkageHelperTraits {
   static Register ReturnValueReg() { return x0; }
   static Register ReturnValue2Reg() { return x1; }
   static Register JSCallFunctionReg() { return x1; }
   static Register ContextReg() { return cp; }
   static Register RuntimeCallFunctionReg() { return x1; }
   static Register RuntimeCallArgCountReg() { return x0; }
   static RegList CCalleeSaveRegisters() {
     // TODO(dcarney): correct callee saved registers.
     return 0;
@@ skipping 27 matching lines @@
       this->info_->zone(), descriptor, stack_parameter_count);
 }
 
 
 CallDescriptor* Linkage::GetSimplifiedCDescriptor(
     Zone* zone, int num_params, MachineRepresentation return_type,
     const MachineRepresentation* param_types) {
   return LinkageHelper::GetSimplifiedCDescriptor<LinkageHelperTraits>(
       zone, num_params, return_type, param_types);
 }
+
+#endif  // V8_TURBOFAN_TARGET
 }
 }
 }  // namespace v8::internal::compiler