title: configure: error: X11 library not found in Mountain Lion
body: <p>I'm trying to install the FORTRAN program rmodel described at <a href="http://www.ucm.es/info/Astrof/software/rmodel/rmodel.html" rel="nofollow noreferrer">http://www.ucm.es/info/Astrof/software/rmodel/rmodel.html</a></p>
  
  <p>./configure fails with the following error:</p>
  
  <pre><code>phym-ssweet2:rmodel-3.2.0 seasto$ sudo ./configure F77=gfortran
  checking for a BSD-compatible install... /usr/bin/install -c
  checking whether build environment is sane... yes
  checking for a thread-safe mkdir -p... ./install-sh -c -d
  checking for gawk... no
  checking for mawk... no
  checking for nawk... no
  checking for awk... awk
  checking whether make sets $(MAKE)... yes
  checking whether the Fortran 77 compiler works... yes
  checking for Fortran 77 compiler default output file name... a.out
  checking for suffix of executables... 
  checking whether we are cross compiling... no
  checking for suffix of object files... o
  checking whether we are using the GNU Fortran 77 compiler... yes
  checking whether gfortran accepts -g... yes
  checking uname -s for detecting host operating system... Darwin
  LDFLAGS set to... -L/opt/local/lib
  checking for style of include used by make... GNU
  checking for gcc... gcc
  checking whether we are using the GNU C compiler... yes
  checking whether gcc accepts -g... yes
  checking for gcc option to accept ISO C89... none needed
  checking dependency style of gcc... none
  checking for main in -lX11... no
  configure: error: X11 library not found
  </code></pre>
  
  <p>I tried pointing ./configure to the libraries using <code>export CPPFLAGS=-I/opt/X11/include</code> and <code>export CPPFLAGS=-I/opt/X11/include LDFLAGS=-L/opt/X11/lib</code> but to no avail. (These suggestions from <a href="https://stackoverflow.com/questions/12027868/mountain-lion-x11-libraries-cant-configure">Mountain Lion X11 libraries can&#39;t ./configure</a> and <a href="https://stackoverflow.com/questions/11664835/mountain-lion-rvm-install-1-8-7-x11-error">Mountain Lion rvm install 1.8.7 x11 error</a>)</p>
  
  <p>Any suggestions would be greatly appreciated.</p>