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/LambdaTests/lambda_capture_local_by_ref.cpp

@@ -0,0 +1,23 @@
+/*
+ * Copyright (c) 2024, Matthew Olsson <mattco@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+// RUN: %clang++ -cc1 -verify %plugin_opts% %s 2>&1
+
+#include <AK/Function.h>
+
+// expected-note@+1 {{Annotate the parameter with NOESCAPE if the lambda will not outlive the function call}}
+void take_fn(Function<void()>) { }
+
+void test()
+{
+    // expected-note@+1 {{Annotate the variable declaration with IGNORE_USE_IN_ESCAPING_LAMBDA if it outlives the lambda}}
+    int a = 0;
+
+    // expected-warning@+1 {{Variable with local storage is captured by reference in a lambda that may be asynchronously executed}}
+    take_fn([&a] {
+        (void)a;
+    });
+}