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

src/arm/simulator-arm.cc

 // Copyright 2010 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 11 matching lines @@
 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 // 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 <stdlib.h>
 #include <cstdarg>
 #include "v8.h"
 
+#if defined(V8_TARGET_ARCH_ARM)
+
 #include "disasm.h"
 #include "assembler.h"
 #include "arm/constants-arm.h"
 #include "arm/simulator-arm.h"
 
 #if !defined(__arm__)
 
 // Only build the simulator if not compiling for real ARM hardware.
 namespace assembler {
 namespace arm {
@@ skipping 2682 matching lines @@
   int current_sp = get_register(sp);
   uintptr_t* stack_slot = reinterpret_cast<uintptr_t*>(current_sp);
   uintptr_t address = *stack_slot;
   set_register(sp, current_sp + sizeof(uintptr_t));
   return address;
 }
 
 } }  // namespace assembler::arm
 
 #endif  // __arm__
+
+#endif  // V8_TARGET_ARCH_ARM