Add a C++ backend for LibertyXDR

Also change the C backend so that it also de/serializes
unions without any other fields besides the tag.

tools/lxdrgen-cpp-win32.cpp

@@ -0,0 +1,47 @@
+// lxdrgen-cpp-win32.cpp: Win32 support code for lxdrgen-cpp.awk.
+//
+// Copyright (c) 2023, Přemysl Eric Janouch <p@janouch.name>
+// SPDX-License-Identifier: 0BSD
+#include <windows.h>
+
+#include <climits>
+#include <cstdint>
+#include <string>
+
+namespace LibertyXDR {
+
+bool utf8_to_wstring(const uint8_t *utf8, size_t length, std::wstring &wide) {
+	wide.clear();
+	if (!length)
+		return true;
+	if (length > INT_MAX)
+		return false;
+
+	int size = MultiByteToWideChar(CP_UTF8, MB_ERR_INVALID_CHARS,
+		(LPCCH) utf8, length, nullptr, 0);
+	if (size <= 0)
+		return false;
+
+	wide.resize(size);
+	return !MultiByteToWideChar(CP_UTF8, MB_ERR_INVALID_CHARS,
+		(LPCCH) utf8, length, wide.data(), size);
+}
+
+bool wstring_to_utf8(const std::wstring &wide, std::string &utf8) {
+	utf8.clear();
+	if (wide.empty())
+		return true;
+	if (wide.size() > INT_MAX)
+		return false;
+
+	int size = WideCharToMultiByte(CP_UTF8, WC_ERR_INVALID_CHARS,
+		(LPCWCH) wide.data(), wide.size(), nullptr, 0, NULL, NULL);
+	if (size <= 0)
+		return false;
+
+	utf8.resize(size);
+	return !WideCharToMultiByte(CP_UTF8, WC_ERR_INVALID_CHARS,
+		(LPCWCH) wide.data(), wide.size(), utf8.data(), size, NULL, NULL);
+}
+
+} // namespace LibertyXDR