title: Using cmake, how to link an object file built by an external_project statement into another library?
body: <p>In our project, we want to use a third-party library (A) which is built using autotools and which generates an object file (B) which we need @ link time of one of our libraries (C).</p>
  
  <pre><code>external_project(
      A
      ...
  )
  set_source_files_properties(B PROPERTIES DEPEND A)
  add_library(C ... A)
  add_dependency(C B)
  </code></pre>
  
  <p>I had the impression that this should do the trick, but the cmake command fails by stating that it cannot find file A during the check for add_library.</p>
  
  <p>Any fixes or alternative solutions would be greatly appreciated! (changing the third-party library is not an option)
  thanks!</p>