Allow build-time selection between ia32 and x86_64 in the GYP/Xcode Mac Chromium build

src/ia32/assembler-ia32.cc

 // Copyright (c) 1994-2006 Sun Microsystems Inc.
 // 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.
 //
@@ skipping 18 matching lines @@
 // STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 // ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 // OF THE POSSIBILITY OF SUCH DAMAGE.
 
 // The original source code covered by the above license above has been modified
 // significantly by Google Inc.
 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 
 #include "v8.h"
 
+#if defined(V8_TARGET_ARCH_IA32)
+
 #include "disassembler.h"
 #include "macro-assembler.h"
 #include "serialize.h"
 
 namespace v8 {
 namespace internal {
 
 // -----------------------------------------------------------------------------
 // Implementation of CpuFeatures
 
@@ skipping 2472 matching lines @@
   push_insn[1] = 13;    // Skip over coverage insns.
   if (coverage_log != NULL) {
     fprintf(coverage_log, "%s\n", file_line);
     fflush(coverage_log);
   }
 }
 
 #endif
 
 } }  // namespace v8::internal
+
+#endif  // V8_TARGET_ARCH_IA32