Add ltdl.h shim for Windows

lib/isc/win32/ltdl.h

@@ -0,0 +1,43 @@
+/*
+ * Copyright (C) Internet Systems Consortium, Inc. ("ISC")
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ *
+ * See the COPYRIGHT file distributed with this work for additional
+ * information regarding copyright ownership.
+ */
+
+#pragma once
+
+#include <windows.h>
+
+#define lt_dlhandle    HMODULE
+#define lt_dlinit()    ISC_R_SUCCESS
+#define lt_dlopen(f)   LoadLibraryW(f)
+#define lt_dlsym(h, s) GetProcAddress(h, s)
+#define lt_dlclose(h)  FreeLibrary(h)
+
+_Thread_local LPSTR __dlerror_message[1024] = { 0 };
+
+static const char *
+lt_dlerror(void) {
+	DWORD errorMessageID = GetLastError();
+	if (errorMessageID == 0) {
+		return (NULL);
+	}
+
+	LPSTR messageBuffer = NULL;
+	size_t size = FormatMessageA(
+		FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM |
+			FORMAT_MESSAGE_IGNORE_INSERTS,
+		NULL, errorMessageID, MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
+		(LPSTR)&messageBuffer, 0, NULL);
+
+	strlcpy(__dlerror_message, messageBuffer, sizeof(__dlerror_message));
+
+	LocalFree(messageBuffer);
+
+	return ((const char *)__dlerror_message);
+}