Clean up the usage of V8_TARGET_ARCH_${arch} and V8_HOST_ARCH_${arch}

src/x64/codegen-x64.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
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 #include "v8.h"
 
-#if defined(V8_TARGET_ARCH_X64)
+#if V8_TARGET_ARCH_X64
 
 #include "codegen.h"
 #include "macro-assembler.h"
 
 namespace v8 {
 namespace internal {
 
 // -------------------------------------------------------------------------
 // Platform-specific RuntimeCallHelper functions.
 
@@ skipping 695 matching lines @@
     CodePatcher patcher(sequence, young_length);
     patcher.masm()->call(stub->instruction_start());
     patcher.masm()->nop();
   }
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64