title: process.env.UV_THREADPOOL_SIZE always showing undefined on macos
body: <p>I am running a simple node script - </p>
  
  <pre><code>var fs = require('fs');
  var start = new Date();
  var simulateTime = 1000;
  
  console.log('LIBUV Threads: ', process.env.UV_THREADPOOL_SIZE);
  for (var i = 0; i &lt; 6; i++) {
    setTimeout(function() {
      var end = new Date() - start
      console.info('Execution time: %dms', end)
    }, simulateTime);
  }
  </code></pre>
  
  <p>I have set the following in package.json - </p>
  
  <pre><code>  "main": "index.js",
    "scripts": {
      "test": "echo \"Error: no test specified\" &amp;&amp; exit 1",
      "start": "set UV_THREADPOOL_SIZE=20 &amp; node index.js"
    },
  </code></pre>
  
  <p>However LIBUV threadpool size is always showing undefined. I am running the script by -</p>
  
  <pre><code>npm start
  </code></pre>
  
  <p>and node version is v12.9.1.</p>
  
  <p>Thanks</p>