Move dead submodules in-tree

Signed-off-by: swurl <swurl@swurl.xyz>

externals/oaknut/include/oaknut/oaknut_exception.hpp

@@ -0,0 +1,44 @@
+// SPDX-FileCopyrightText: Copyright (c) 2023 merryhime <https://mary.rs>
+// SPDX-License-Identifier: MIT
+
+#pragma once
+
+#include <exception>
+
+namespace oaknut {
+
+enum class ExceptionType {
+#define OAKNUT_EXCEPTION(tag, str) tag,
+#include "oaknut/impl/oaknut_exception.inc.hpp"
+#undef OAKNUT_EXCEPTION
+};
+
+inline const char* to_string(ExceptionType et)
+{
+    switch (et) {
+#define OAKNUT_EXCEPTION(tag, str) \
+    case ExceptionType::tag:       \
+        return str;
+#include "oaknut/impl/oaknut_exception.inc.hpp"
+#undef OAKNUT_EXCEPTION
+    default:
+        return "unknown ExceptionType";
+    }
+}
+
+class OaknutException : public std::exception {
+public:
+    explicit OaknutException(ExceptionType et)
+        : type{et}
+    {}
+
+    const char* what() const noexcept override
+    {
+        return to_string(type);
+    }
+
+private:
+    ExceptionType type;
+};
+
+}  // namespace oaknut