Update V8 to r4730 as required by WebKit r60469
diff --git a/src/x64/builtins-x64.cc b/src/x64/builtins-x64.cc
index c55a4ea..8099feb 100644
--- a/src/x64/builtins-x64.cc
+++ b/src/x64/builtins-x64.cc
@@ -26,6 +26,9 @@
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 #include "v8.h"
+
+#if defined(V8_TARGET_ARCH_X64)
+
 #include "codegen-inl.h"
 #include "macro-assembler.h"
 
@@ -1296,3 +1299,5 @@
 }
 
 } }  // namespace v8::internal
+
+#endif  // V8_TARGET_ARCH_X64