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

src/mips/builtins-mips.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 "v8.h"
 
+#if defined(V8_TARGET_ARCH_MIPS)
+
 #include "codegen-inl.h"
 #include "debug.h"
 #include "runtime.h"
 
 namespace v8 {
 namespace internal {
 
 
 #define __ ACCESS_MASM(masm)
 
@@ skipping 151 matching lines @@
 void Builtins::Generate_ArgumentsAdaptorTrampoline(MacroAssembler* masm) {
   UNIMPLEMENTED_MIPS();
   __ break_(0x201);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
+#endif  // V8_TARGET_ARCH_MIPS