title: Configure error installing fftw
body: <p>I just followed the instructions <a href="https://solarianprogrammer.com/2016/05/10/compiling-gcc-6-mac-os-x/" rel="nofollow">here</a> to update my gcc. Now I am trying to install FFTW. So I downloaded the filed <a href="http://www.fftw.org/download.html" rel="nofollow">here</a>. After I unzip and navigate to that directory I run this:</p>
  
  <pre><code>./configure  --enable-mpi --enable-threads --enable-openmp
  </code></pre>
  
  <p>But I get the following error:</p>
  
  <pre><code>checking for OpenMP flag of C compiler... unknown
  configure: error: don't know how to enable OpenMP
  </code></pre>
  
  <p>I know OpenMP didn't work before I updated GCC, but it does now if I do this:</p>
  
  <pre><code>export PATH=/usr/local/gcc-6.1.0/bin:$PATH
  gcc-6.1.0 main.c -o main
  </code></pre>
  
  <p>So I'm guessing the problem is that when I try to configure FFTW it is using the default gcc, but I need it to use gcc-6.1.0. How can I do this?</p>