title: Can't compile a C program on a Mac after upgrading to Catalina 10.15
body: <p>There's a previous question <a href="https://stackoverflow.com/questions/52509602/cant-compile-c-program-on-a-mac-after-upgrade-to-mojave">Can't compile C program on a Mac after upgrade to Mojave</a>, and the answers to that have covered most of the variations on what goes wrong.</p>
  
  <p>Now — as of Monday 2019-10-07 — you can upgrade to macOS Catalina 10.15.  Once again, during the upgrade, the <code>/usr/include</code> directory has been blown away by the update, even though XCode 11.0 was installed before upgrading (from Mojave 10.14.6) to Catalina.  Consequently, compilers built to expect that there is a <code>/usr/include</code> directory do not work any longer.</p>
  
  <p>The main recommended step for the Mojave issues — using the command:</p>
  
  <blockquote>
  <pre><code>open /Library/Developer/CommandLineTools/Packages/macOS_SDK_headers_for_macOS_10.14.pkg
  </code></pre>
  </blockquote>
  
  <p>does not work out of the gate because the directory <code>/Library/Developer/CommandLineTools/Packages/</code> does not exist (so there's not yet a <code>.pkg</code> file to open).</p>
  
  <p>Is there a good (official) way to create and populate the directory <code>/usr/include</code>?</p>