title: mac error: pkg-config not found (even if pkg-config is already installed)
body: <p>I have read several posts about this.<br>
  But they didn't solved from mine.</p>
  
  <p>Please see the information </p>
  
  <pre><code>brew install pkg-config
  </code></pre>
  
  <p>Finish install then</p>
  
  <pre><code>Rangers-iMac:dash ranger$ which pkg-config
  /usr/local/bin/pkg-config
  </code></pre>
  
  <p>It means pkg-config is installed.</p>
  
  <pre><code>Rangers-iMac:dash ranger$ ./configure
  ...
  checking for exit in -lboost_chrono-mt... yes
  checking whether the Boost::Unit_Test_Framework library is available... yes
  checking for dynamic linked boost test... yes
  configure: error: pkg-config not found.
  </code></pre>
  
  <p>it means configure can't find pkg-config.</p>
  
  <p>I think the problem is in PATH, but I can't figure out how to fix it.</p>