Move dependencies in 'external' directory and pdate git submodules

external/Catch2/fuzzing/NullOStream.h

@@ -0,0 +1,28 @@
+
+//              Copyright Catch2 Authors
+// Distributed under the Boost Software License, Version 1.0.
+//   (See accompanying file LICENSE.txt or copy at
+//        https://www.boost.org/LICENSE_1_0.txt)
+
+// SPDX-License-Identifier: BSL-1.0
+
+#pragma once
+
+#include <ostream>
+#include <streambuf>
+
+// from https://stackoverflow.com/a/8244052
+class NullStreambuf : public std::streambuf {
+  char dummyBuffer[64];
+
+protected:
+  virtual int overflow(int c) override final;
+};
+
+class NullOStream final : private NullStreambuf, public std::ostream {
+public:
+  NullOStream() : std::ostream(this) {}
+  NullStreambuf *rdbuf() { return this; }
+  virtual void avoidOutOfLineVirtualCompilerWarning();
+};
+