ClangPlugins: Add LLVM lit test suite

Author: https://github.com/mattco98
Commit: 46ee2b5f06
Pull-request: https://github.com/SerenityOS/serenity/pull/24027
Reviewed-by: https://github.com/ADKaster ✅
Reviewed-by: https://github.com/nico

Tests/ClangPlugins/LibJSGCTests/non_cell_class.cpp

@@ -0,0 +1,14 @@
+/*
+ * Copyright (c) 2024, Matthew Olsson <mattco@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+// RUN: %clang++ -cc1 -verify %plugin_opts% %s 2>&1
+// expected-no-diagnostics
+
+#include <LibJS/Runtime/Object.h>
+
+class NonCell {
+    JS::GCPtr<JS::Object> m_object;
+};