Backend: Create "backend" folder

similar to the "frontend" folder

src/backend/x64/exception_handler_generic.cpp

@@ -0,0 +1,21 @@
+/* This file is part of the dynarmic project.
+ * Copyright (c) 2016 MerryMage
+ * This software may be used and distributed according to the terms of the GNU
+ * General Public License version 2 or any later version.
+ */
+
+#include "backend/x64/block_of_code.h"
+
+namespace Dynarmic::BackendX64 {
+
+struct BlockOfCode::ExceptionHandler::Impl final {
+};
+
+BlockOfCode::ExceptionHandler::ExceptionHandler() = default;
+BlockOfCode::ExceptionHandler::~ExceptionHandler() = default;
+
+void BlockOfCode::ExceptionHandler::Register(BlockOfCode&) {
+    // Do nothing
+}
+
+} // namespace Dynarmic::BackendX64