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

src/x64/disasm-x64.cc

 // Copyright 2009 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 12 matching lines @@
 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 // THEORY OF LIABILITY, WHETHER IN CONTRACT, 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.
 
 #include <assert.h>
 #include <stdio.h>
 #include <stdarg.h>
 
 #include "v8.h"
+
+#if defined(V8_TARGET_ARCH_X64)
+
 #include "disasm.h"
 
 namespace disasm {
 
 enum OperandType {
   UNSET_OP_ORDER = 0,
   // Operand size decides between 16, 32 and 64 bit operands.
   REG_OPER_OP_ORDER = 1,  // Register destination, operand source.
   OPER_REG_OP_ORDER = 2,  // Operand destination, register source.
   // Fixed 8-bit operands.
@@ skipping 1621 matching lines @@
       fprintf(f, "%02x", *bp);
     }
     for (int i = 6 - static_cast<int>(pc - prev_pc); i >= 0; i--) {
       fprintf(f, "  ");
     }
     fprintf(f, "  %s\n", buffer.start());
   }
 }
 
 }  // namespace disasm
+
+#endif  // V8_TARGET_ARCH_X64