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

src/x64/assembler-x64.cc

 // Copyright 2009 the V8 project authors. All rights reserved.
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 // 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
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 //       with the distribution.
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 //       contributors may be used to endorse or promote products derived
 //       from this software without specific prior written permission.
 //
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 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 #include "v8.h"
 
+#if defined(V8_TARGET_ARCH_X64)
+
 #include "macro-assembler.h"
 #include "serialize.h"
 
 namespace v8 {
 namespace internal {
 
 // -----------------------------------------------------------------------------
 // Implementation of CpuFeatures
 
 // The required user mode extensions in X64 are (from AMD64 ABI Table A.1):
@@ skipping 2693 matching lines @@
     written_position_ = current_position_;
   }
 }
 
 
 const int RelocInfo::kApplyMask = RelocInfo::kCodeTargetMask |
                                   1 << RelocInfo::INTERNAL_REFERENCE |
                                   1 << RelocInfo::JS_RETURN;
 
 } }  // namespace v8::internal
+
+#endif  // V8_TARGET_ARCH_X64