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

src/ia32/full-codegen-ia32.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
 //       disclaimer in the documentation and/or other materials provided
 //       with the distribution.
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 //       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,
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 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 #include "v8.h"
 
+#if defined(V8_TARGET_ARCH_IA32)
+
 #include "codegen-inl.h"
 #include "compiler.h"
 #include "debug.h"
 #include "full-codegen.h"
 #include "parser.h"
 #include "scopes.h"
 
 namespace v8 {
 namespace internal {
 
@@ skipping 1965 matching lines @@
   __ add(Operand(edx), Immediate(masm_->CodeObject()));
   __ mov(Operand(esp, 0), edx);
   // And return.
   __ ret(0);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
+
+#endif // V8_TARGET_ARCH_IA32