title: Include path in makefile to include subdirectories
body: <p>I have a directory which internal contains sub directories. I want to include the parent directory as include path in make file for header files. Is there a syntax so that all the sub directories are searched for the header files.</p>
  
  <pre><code>[EDIT] Posting the question in more detail
  There are three sub folders in a parent folder
  parentFolder/child1
  parentFolder/child2
  parentFolder/child3
  
  There are header files in each all subfolders
  
  Using -I option in makefile for header file path, i have to use
  HEADER_PATH += -I./parentFolder
  HEADER_PATH += -I./parentFolder/child1
  HEADER_PATH += -I./parentFolder/child2
  HEADER_PATH += -I./parentFolder/child3
  
  Is there any way I can mention only the parent folder , but the search for header files will happen in all the subfolders also
  </code></pre>