title: install a EXCLUDE_FROM_ALL subdirectory
body: <p>I have a project <code>A</code> that uses some targets defined in project <code>B</code>. Hence I did <code>add_subdirectory(&lt;PATH_TO B&gt; EXCLUDE_FROM_ALL)</code> to include the subdirectory. Now, I create install targets using components and there are some install components in <code>A</code> that require targets from <code>B</code> too. But, due to <code>EXCLUDE_FROM_ALL</code>, the <code>cmake_install.cmake</code> for <code>A</code> does not include that of <code>B</code>. How should I approach this?</p>