title: CMake can't find IMPORTED library
body: <p>In <code>foo/CMakeLists.txt</code>, based on <a href="http://www.cmake.org/pipermail/cmake/2008-June/022256.html" rel="noreferrer">this</a> and <a href="http://www.cmake.org/Wiki/CMake/Tutorials/Exporting_and_Importing_Targets" rel="noreferrer">this</a>, I have the following</p>
  
  <pre><code>SET (EXTERNAL_LIB_ROOT "../../external_libs/")
  
  ADD_LIBRARY (avcodec-debug STATIC IMPORTED)
  
  SET_PROPERTY (
      TARGET avcodec-debug PROPERTY IMPORTED_LOCATION
      ${EXTERNAL_LIB_ROOT}/libavcodec-0.8.10.a)
  </code></pre>
  
  <p>In <code>bar/CMakeLists.txt</code> I have this:</p>
  
  <pre><code># old way uses system libraries
  #TARGET_LINK_LIBRARIES (bar avformat avcodec avutil)
  
  # new way uses local debug builds
  TARGET_LINK_LIBRARIES (bar avformat avcodec-debug avutil)
  </code></pre>
  
  <p>When I run <code>make</code> I get</p>
  
  <pre><code>/usr/bin/ld: cannot find -lavcodec-debug
  </code></pre>
  
  <p>If I revert to the old way, build, touch <code>foo/CMakeLists.txt</code> and rebuild, CMake's configuration output indicates that avcodec-debug <em>is</em> being found by the build system.</p>
  
  <p>So why can't I add it as a dependency?</p>