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

src/x64/frames-x64.cc

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 #include "v8.h"
 
-#if defined(V8_TARGET_ARCH_X64)
+#if V8_TARGET_ARCH_X64
 
 #include "assembler.h"
 #include "assembler-x64.h"
 #include "assembler-x64-inl.h"
 #include "frames.h"
 
 namespace v8 {
 namespace internal {
 
 
 Register JavaScriptFrame::fp_register() { return rbp; }
 Register JavaScriptFrame::context_register() { return rsi; }
 
 
 Register StubFailureTrampolineFrame::fp_register() { return rbp; }
 Register StubFailureTrampolineFrame::context_register() { return rsi; }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64