Implement correct OS and CC detection.

test/cctest/test-assembler-x64.cc

 // Copyright 2009 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 418 matching lines @@
       Code::ComputeFlags(Code::STUB),
       v8::internal::Handle<Code>())->ToObjectChecked());
   CHECK(code->IsCode());
 
   F0 f = FUNCTION_CAST<F0>(code->entry());
   int res = f();
   CHECK_EQ(42, res);
 }
 
 
-#ifdef __GNUC__
+#if V8_CC_GNU
 #define ELEMENT_COUNT 4
 
 void DoSSE2(const v8::FunctionCallbackInfo<v8::Value>& args) {
   CcTest::InitializeVM();
   v8::HandleScope scope(CcTest::isolate());
   v8::internal::byte buffer[1024];
 
   CHECK(args[0]->IsArray());
   v8::Local<v8::Array> vec = v8::Local<v8::Array>::Cast(args[0]);
   CHECK_EQ(ELEMENT_COUNT, vec->Length());
@@ skipping 64 matching lines @@
   }
 
   v8::Local<v8::Value> args[] = { v8_vec };
   v8::Local<v8::Value> result = foo->Call(global_object, 1, args);
 
   // The mask should be 0b1000.
   CHECK_EQ(8, result->Int32Value());
 }
 
 #undef ELEMENT_COUNT
-#endif  // __GNUC__
+#endif  // V8_CC_GNU
 
 
 #undef __