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

src/x64/macro-assembler-x64.cc

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 #include "v8.h"
 
-#if defined(V8_TARGET_ARCH_X64)
+#if V8_TARGET_ARCH_X64
 
 #include "bootstrapper.h"
 #include "codegen.h"
 #include "assembler-x64.h"
 #include "macro-assembler-x64.h"
 #include "serialize.h"
 #include "debug.h"
 #include "heap.h"
 
 namespace v8 {
@@ skipping 4660 matching lines @@
   j(greater, &no_info_available);
   CompareRoot(MemOperand(scratch_reg, -AllocationSiteInfo::kSize),
               Heap::kAllocationSiteInfoMapRootIndex);
   bind(&no_info_available);
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64