Motivation:

`URLSession` elusively crashes due to race conditions in OpenSSL <1.1.0 when calling `curl_multi_cleanup` concurrently on different threads.

Modifications:

- Add `CFURLSessionSSLVersion CFURLSessionSSLVersionInfo(void)` for detecting the OpenSSL version in use.
- Adjust `_MultiHandle.deinit` to use a process-wide lock to serialize `curl_multi_cleanup` calls for environments with OpenSSL <1.1.0.

Result:

Prevents the crash while avoiding unnecessary performance overhead for newer OpenSSL versions which are thread-safe.

Testing:

Passing existing tests is sufficient. However, without this patch, the code snippet below crashes about once in 20 runs on Amazon Linux 2
> $ curl --version
> _curl 8.3.0 (aarch64-koji-linux-gnu) libcurl/8.3.0 OpenSSL/1.0.2k-fips zlib/1.2.7 libidn2/2.3.0 libpsl/0.21.5 (+libidn2/2.3.0) libssh2/1.4.3 nghttp2/1.41.0 OpenLDAP/2.4.44_
> _Release-Date: 2023-09-13_
...
```
DispatchQueue.concurrentPerform(iterations: 100) { _ in
    let session: URLSession = URLSession(configuration: URLSessionConfiguration.default)
    DispatchQueue.concurrentPerform(iterations: 100) { _ in
        _ = session
    }
}
```