title: Autotools include path
body: <p>I have a directory structure like </p>
  
  <pre><code>Makefile.am
  Configure.ac
           src/
               hello.c
               Makefile.am
  
           include/
               hello.h
  </code></pre>
  
  <p>How to specify the include path in Makefile.am of src so that it includes header files from include/ dir as well as c file depends on header file. 
  So if I modify any .h file it force to recompile .cc file. </p>
  
  <p>Defining AM_CPPFLAGS' is giving warning </p>
  
  <pre><code>configure.ac:5: warning: macro `AM_CPPFLAGS' not found in library
  </code></pre>