title: autoconf & automake versus -O2 versus -O3
body: <p>My configure.ac contains</p>
  
  <pre><code>AC_PROG_CXX
  </code></pre>
  
  <p>and my Makefile.am contains</p>
  
  <pre><code>AM_CXXFLAGS= -Werror -O3
  </code></pre>
  
  <p>and the resulting 'configure' script keeps on adding -O2 to the mix in addition to O3.</p>
  
  <p>I have this suspicion that I'm supposed to do something in configure.ac to declare my preference for O3, but I can't find it in the doc. How do I tell it that I want to control the optimization level?</p>