title: error: target Objective-C runtime differs in PCH file vs. current file
body: <p>I'm trying to compile Objective-C or <code>.m</code> file using command-line (generated by <code>CMake</code>) for <code>Catalyst</code>, but am stuck with two compile errors!</p>
  <p>1. Whenever I enable <code>Catalyst</code> with one of below flags:</p>
  <pre><code>-target x86_64-apple-ios-macabi
  -target x86_64-apple-ios13.0-macabi
  -target x86_64-apple-ios13.5-macabi
  -target x86_64-apple-ios13.7-macabi
  </code></pre>
  <p>2. Then force rebuild (click <code>Clean Build Folder</code>, then <code>Build</code>).</p>
  <p>3. The build fails with error:</p>
  <pre><code>fatal error: 'UIKit/UIKit.h' file not found
  </code></pre>
  <p>4. But once I switch to <code>13.6</code>, I mean, change the flag to:</p>
  <pre><code>-target x86_64-apple-ios13.6-macabi
  </code></pre>
  <p>5. Then force-rebuild, I get a new error:</p>
  <pre><code>error: target Objective-C runtime differs in PCH file vs. current file
  </code></pre>
  <blockquote>
  <p><strong>Note</strong> that I am not using any PCH file, and both errors seem completely confusing.</p>
  </blockquote>
  <p>Also, I searched and found <a href="https://stackoverflow.com/a/63360945/8740349">post similar to second error</a>, but the fix suggested (namely, switching to <code>13.6</code>) is the cause of the second error.
  (Was supposed to fix it, yet is triggering it).</p>