title: CMake imported target includes non-existent path
body: <p>I've followed the steps described in <a href="https://stackoverflow.com/questions/59009607/linking-against-gtest-fails">Linking against GTest fails</a>, and get this error.</p>
  
  <pre><code>CMake Error in src/impl/data_structures/simple_tree/CMakeLists.txt:
        Imported target "GTest::GTest" includes non-existent path
  
          "~/local/include/"
  </code></pre>
  
  <p>Further messages include:</p>
  
  <pre><code>in its INTERFACE_INCLUDE_DIRECTORIES.  Possible reasons include:
  
    * The path was deleted, renamed, or moved to another location.
  
    * An install or uninstall procedure did not complete successfully.
  
    * The installation package was faulty and references files it does not
    provide.
  </code></pre>
  
  <p>EDIT: Although it loses "generality", I replaced the <code>~/</code> path with
  the full path, and then get this error:</p>
  
  <pre><code>/usr/bin/ld: cannot find /home/myself/local/lib/: File format not recognized
  </code></pre>
  
  <p>The path exists, to be sure.</p>