Add unit tests for the tid allocator (#2519)

Add simple infrastructure to add more unit tests in the future. At the moment tests
are only executed on Linux, but can be extended to other platforms if needed.

Use https://github.com/google/googletest/ as a framework.

tests/unit/main.cpp

@@ -0,0 +1,21 @@
+/*
+ * Copyright (C) 2023 Amazon.com Inc. or its affiliates. All rights reserved.
+ * SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+ */
+#include <gtest/gtest.h>
+#include "wasm_runtime_common.h"
+
+int
+main(int argc, char **argv)
+{
+    ::testing::InitGoogleTest(&argc, argv);
+
+    if (!wasm_runtime_init()) {
+        return -1;
+    }
+
+    int ret = RUN_ALL_TESTS();
+    wasm_runtime_destroy();
+
+    return ret;
+}