externals: Add catch2 v3.2.1

Merge commit '6879e5bb1c' as 'externals/catch'

externals/catch/tests/ExtraTests/X11-DisableStringification.cpp

@@ -0,0 +1,27 @@
+
+//              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
+
+/**\file
+ * Test that stringification of original expression can be disabled.
+ *
+ * This is a workaround for VS 2017, 2019 issue with Raw String literals
+ * and preprocessor token pasting.
+ */
+
+
+#include <catch2/catch_test_macros.hpp>
+
+namespace {
+    struct Hidden {};
+
+    bool operator==(Hidden, Hidden) { return true; }
+}
+
+TEST_CASE("DisableStringification") {
+    REQUIRE( Hidden{} == Hidden{} );
+}