Add compilation guard to new x64-only file, for Mac platform.

Review URL: http://codereview.chromium.org/6249016

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6462 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/x64/lithium-gap-resolver-x64.cc

@@ -25,6 +25,10 @@
 // (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_X64)
+
 #include "x64/lithium-gap-resolver-x64.h"
 #include "x64/lithium-codegen-x64.h"
 
@@ -312,3 +316,5 @@ void LGapResolver::EmitSwap(int index) {
 #undef __
 
 } }  // namespace v8::internal
+
+#endif  // V8_TARGET_ARCH_X64