title: CMake : Add subdirectories to custom target and adding custom target to VS solution
body: <p>Using CMake, I am trying to this: </p>
  
  <ol>
  <li><p>I need a custom build target (I know, I it can create it with custom_target), but I want it to get added to the visual studio solution. Now when I create a custom target I see the project file in the folder but it is not shown/added in the VS solution, when I open the VS solution in VS IDE. </p></li>
  <li><p>I need to add subdirectories (which has CMakeLists.txt in them) to the custom target, so that these projects will get added to the custom target and when the custom target is build these projects will get build. </p></li>
  </ol>
  
  <p>Basically another line of build like ALL_BUILD. When ALL_BUILD is build, only the projects (subdirectories) added to it will get build. When the custom target is build only the projects (subdirectories) added to the custom target will get build. </p>
  
  <p>Is it possible to do something like this? </p>
  
  <p>Thank you so much for your time and help! </p>
  
  <p>--RC</p>