Adding 'x64' backend.

Does not compile.

src/xenia/cpu/x64/x64_backend.h

@@ -0,0 +1,39 @@
+/**
+ ******************************************************************************
+ * Xenia : Xbox 360 Emulator Research Project                                 *
+ ******************************************************************************
+ * Copyright 2013 Ben Vanik. All rights reserved.                             *
+ * Released under the BSD license - see LICENSE in the root for more details. *
+ ******************************************************************************
+ */
+
+#ifndef XENIA_CPU_X64_X64_BACKEND_H_
+#define XENIA_CPU_X64_X64_BACKEND_H_
+
+#include <xenia/common.h>
+
+#include <xenia/cpu/backend.h>
+
+
+namespace xe {
+namespace cpu {
+namespace x64 {
+
+
+class X64Backend : public Backend {
+public:
+  X64Backend();
+  virtual ~X64Backend();
+
+  virtual JIT* CreateJIT(xe_memory_ref memory, sdb::SymbolTable* sym_table);
+
+protected:
+};
+
+
+}  // namespace x64
+}  // namespace cpu
+}  // namespace xe
+
+
+#endif  // XENIA_CPU_X64_X64_BACKEND_H_