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

src/platform-macos.cc

 // Copyright 2012 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 565 matching lines @@
   buffer[kBufferSize - 1] = '\0';
   char* period_pos = strchr(buffer, '.');
   *period_pos = '\0';
   int kernel_version_major =
       static_cast<int>(strtol(buffer, NULL, 10));  // NOLINT
   // The constants below are taken from pthreads.s from the XNU kernel
   // sources archive at www.opensource.apple.com.
   if (kernel_version_major < 11) {
     // 8.x.x (Tiger), 9.x.x (Leopard), 10.x.x (Snow Leopard) have the
     // same offsets.
-#if defined(V8_HOST_ARCH_IA32)
+#if V8_HOST_ARCH_IA32
     kMacTlsBaseOffset = 0x48;
 #else
     kMacTlsBaseOffset = 0x60;
 #endif
   } else {
     // 11.x.x (Lion) changed the offset.
     kMacTlsBaseOffset = 0;
   }
 
   Release_Store(&tls_base_offset_initialized, 1);
@@ skipping 147 matching lines @@
   limit_mutex = CreateMutex();
 }
 
 
 void OS::TearDown() {
   delete limit_mutex;
 }
 
 
 } }  // namespace v8::internal