title: Installing psycopg2 command 'gcc' failed with exit status 1
body: <p>I'm trying to install psycopg2 but 
  <code>pip install psycopg2</code>  brings to error: command 'gcc' failed with exit status 1</p>
  
  <p>Command line tools are installed</p>
  
  <p>MacOS 10.15</p>