title: Clion is not showing errors for header files without source file
body: <p>I recently switched from visual studio to clion cause I'm used to jetbrains products more. I noticed, that header file needs to have source file to show me errors.</p>
  <p><a href="https://i.stack.imgur.com/LWO1w.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/LWO1w.png" alt="enter image description here" /></a></p>
  <p>This line is clearly wrong, but clion doesn't care. My cmake:</p>
  <pre><code>set(ALL_FILES
          ....
          src/....../ttest.h)
  </code></pre>
  <p>When I add a .cpp file:</p>
  <pre><code>...
  src/....../ttest.cpp src/....../ttest.h
  </code></pre>
  <p>It works just fine:</p>
  <p><a href="https://i.stack.imgur.com/laaxz.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/laaxz.png" alt="enter image description here" /></a></p>
  <p>Why is that? I have a lot of header-only files. Thanks.</p>