title: GMP & MPFR not found by cmake, but are installed
body: <p>I'm trying to compile the plll library which require boost, GMP and MPFR on mac os X 10.11. </p>
  
  <p>I've installed boost, GMP and MPFR by homebrew, then i've launched cmake in a dir build in plll, but I get that error :</p>
  
  <pre><code> By not providing "FindMPFR.cmake" in CMAKE_MODULE_PATH this project has
   asked CMake to find a package configuration file provided by "MPFR", but
   CMake did not find one.
  
   Could not find a package configuration file provided by "MPFR" with any of
  the following names:
  
  MPFRConfig.cmake
  mpfr-config.cmake
  
  Add the installation prefix of "MPFR" to CMAKE_PREFIX_PATH or set
  "MPFR_DIR" to a directory containing one of the above files.  If "MPFR"
  provides a separate development package or SDK, be sure it has been
  installed.
  </code></pre>
  
  <p>And the same for GMP if I change the order of GMP and MPFR in the Librairies.txt used by cmake.</p>
  
  <p>After that i've install the librairies by hand and they are in/usr/local/include. The make check of GMP is perfect so I guess that the installation is ok.</p>
  
  <p>But still the same error message. I've also tried to add a FindMPFR.cmake file but no change at all.</p>
  
  <p>Here is the part of the Libraries.txt which is concerned:</p>
  
  <pre><code>find_package(MPFR REQUIRED)
  include_directories(${MPFR_INCLUDES})
  if(NOT MPFR_FOUND)
      message(FATAL_ERROR "Could not find MPFR!")
  endif(NOT MPFR_FOUND)
  set(libraries ${libraries} ${MPFR_LIBRARIES})
  set(libraries_shared ${libraries_shared} ${MPFR_LIBRARIES})
  
  find_package(GMP REQUIRED)
  include_directories(${GMP_INCLUDE_DIR})
  if(NOT (GMP_INCLUDE_DIR AND GMP_LIBRARIES))
      message(FATAL_ERROR "Could not find GMP!")
  endif(NOT (GMP_INCLUDE_DIR AND GMP_LIBRARIES))
  set(libraries ${libraries} ${GMP_LIBRARIES})
  set(libraries_shared ${libraries_shared} ${GMP_LIBRARIES})
  </code></pre>
  
  <p>The strange part of that is that I've no problem with Boost...</p>