Adding 'x64' backend.

Does not compile.

src/xenia/cpu/x64/x64_emit.h

@@ -0,0 +1,43 @@
+/**
+ ******************************************************************************
+ * 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_EMIT_H_
+#define XENIA_CPU_X64_X64_EMIT_H_
+
+#include <xenia/cpu/ppc/instr.h>
+#include <xenia/cpu/ppc/state.h>
+#include <xenia/cpu/x64/x64_emitter.h>
+
+
+namespace xe {
+namespace cpu {
+namespace x64 {
+
+
+void X64RegisterEmitCategoryALU();
+void X64RegisterEmitCategoryControl();
+void X64RegisterEmitCategoryFPU();
+void X64RegisterEmitCategoryMemory();
+
+
+#define XEEMITTER(name, opcode, format) int InstrEmit_##name
+
+#define XEREGISTERINSTR(name, opcode) \
+    RegisterInstrEmit(opcode, (InstrEmitFn)InstrEmit_##name);
+
+#define XEINSTRNOTIMPLEMENTED()
+//#define XEINSTRNOTIMPLEMENTED XEASSERTALWAYS
+
+
+}  // namespace x64
+}  // namespace cpu
+}  // namespace xe
+
+
+#endif  // XENIA_CPU_X64_X64_EMIT_H_