title: Using same CFLAGS on Makefile.am in each subdirectories (sub-make)
body: <p>I have a project with a Makefile.am in each of the multiple subdirectories.</p>
  
  <p>How do you propagate a <code>AM_CFLAGS</code> variable setting from that parent Makefile.am to other subdirectories' Makefile.am (sub-make)?</p>
  
  <p>I'm aware of the following methods:</p>
  
  <ul>
  <li><code>export</code> a variable</li>
  <li><code>include</code> statement to a common <code>${top_srcdir}/Makefile_cflags.am</code> file.</li>
  <li><code>MAKEFLAGS</code></li>
  </ul>
  
  <p>Recursive make is not an option and I'm shying away from <code>include</code> and <code>MAKEFLAGS</code> statement approaches.</p>
  
  <p>The GNU manual doesn't seem to clearly outline about propagating compiler/linker settings to sub-make.</p>