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

src/arm/cpu-arm.cc

 // Copyright 2006-2009 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 14 matching lines @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 // CPU specific code for arm independent of OS goes here.
 #ifdef __arm__
 #include <sys/syscall.h>  // for cache flushing.
 #endif
 
 #include "v8.h"
 
+#if defined(V8_TARGET_ARCH_ARM)
+
 #include "cpu.h"
 #include "macro-assembler.h"
 
 #ifndef __arm__
 #include "simulator-arm.h"  // for cache flushing.
 #endif
 
 namespace v8 {
 namespace internal {
 
@@ skipping 84 matching lines @@
 
 void CPU::DebugBreak() {
 #if !defined (__arm__) || !defined(CAN_USE_ARMV5_INSTRUCTIONS)
   UNIMPLEMENTED();  // when building ARM emulator target
 #else
   asm volatile("bkpt 0");
 #endif
 }
 
 } }  // namespace v8::internal
+
+#endif  // V8_TARGET_ARCH_ARM