title: What are legal items in the INTERFACE_LINK_LIBRARIES property?
body: <p>My expectations are, that the items in the target property <code>INTERFACE_LINK_LIBRARIES</code> are other targets. However when I use on Linux for the official Threads package.</p>
  
  <pre><code>find_package(Threads)
  get_property(libs TARGET Threads::Threads PROPERTY INTERFACE_LINK_LIBRARIES)
  </code></pre>
  
  <p>libs ist set to <code>-lpthread</code>, which seems to be a linker flag, not a target.
  Is this correct?</p>