title: XCode Build Error - missing required module 'Algorithms'
body: <p><strong>Background</strong></p>
  <ol>
  <li>I was trying to upgrade old project from xcode 11.3 into xcode 12.4. The code is still on Swift 4.2</li>
  <li>When try to build (any iOS device - arm64) every swift file in the project got same error:</li>
  </ol>
  <pre class="lang-none prettyprint-override"><code> &lt;unknown\&gt;:0: error: missing required module '**Algorithms**'
  </code></pre>
  <p><img src="https://i.stack.imgur.com/PdvFF.png" alt="" />
  3. After try to rebuild using xcode 11.3, then i found out that <strong>arm64-apple-ios.swiftinterface</strong> is actually adding <strong>import 'Algorithms'</strong> in top of the file <img src="https://i.stack.imgur.com/TuRCZ.png" alt="" /></p>
  <blockquote>
  <p>//swift-interface-format-version: 1.0 <br>
  // swift-compiler-version: Apple Swift version 5.3.1 (swiftlang-1200.8.41 clang-1200.0.32.8) <br>
  // swift-module-flags: -target arm64-apple-ios9.0 -enable-objc-interop -enable-librar -swift-version 5 -enforce-exclusivi checked -Onone -module-name Charts <br>
  import Algorithms <br>
  @_exported import Charts <br>
  import CoreGraphics</p>
  </blockquote>
  <p><strong>Question</strong></p>
  <ul>
  <li><p>How to add this algorithms.h into the project/compilation process, so the project able to compile?</p>
  </li>
  <li><p>What caused the compiler to add this? is it because the build setting &gt; Swift Language Version &gt; Swift 4.2 ?</p>
  </li>
  </ul>
  <p><strong>What i have tried</strong></p>
  <ul>
  <li>reinstall XCode Command Line Tools 12.4</li>
  <li>Build Settings-&gt;Apple Clang - Language-C++ -&gt;C++ Standard Library(libc++) refference:[https://stackoverflow.com/questions/25649385/algorithm-file-not-found]</li>
  </ul>