title: clang: error: : errorunsupported option '-fopenmp' on Mac OSX El Capitan building XGBoost
body: <p>I'm trying to build <a href="http://xgboost.readthedocs.org/" rel="noreferrer">XGBoost</a> package for Python following <a href="http://xgboost.readthedocs.org/en/latest/build.html#building-on-osx" rel="noreferrer">these instructions</a>: </p>
  
  <blockquote>
    <p>Here is the complete solution to use OpenMP-enabled compilers to install XGBoost. Obtain gcc-5.x.x with openmp support by <code>brew install gcc --without-multilib</code>. (brew is the de facto standard of apt-get on OS X. So installing HPC separately is not recommended, but it should work.):</p>
  </blockquote>
  
  <pre><code>git clone --recursive https://github.com/dmlc/xgboost
  cd xgboost; cp make/config.mk ./config.mk; make -j4
  </code></pre>
  
  <p>This error occurss precisely in the <code>make -j4</code> command.</p>
  
  <p>Searching beforenad, I've tried these two solutions (<a href="https://stackoverflow.com/questions/19649634/clang-error-unsupported-option-static-libgcc-on-mac-osx-mavericks">1</a> and <a href="https://stackoverflow.com/questions/19351219/cuda-clang-and-os-x-mavericks">2</a>), to no avail, except for the part to installing another gcc by fear of messing up everything.</p>
  
  <p>Below is the <code>make</code> configuration file. It has none suspicious about.</p>
  
  <pre><code>#-----------------------------------------------------
  #  xgboost: the configuration compile script
  #
  #  If you want to change the configuration, please use the following
  #  steps. Assume you are on the root directory of xgboost.
  #  First copy the this file so that any local changes will be ignored by git
  #
  #  $ cp make/config.mk .
  #
  #  Next modify the according entries, and then compile by
  #
  #  $ make
  #
  #  or build in parallel with 8 threads
  #
  #  $ make -j8
  #----------------------------------------------------
  
  # choice of compiler, by default use system preference.
  # export CC = gcc
  # export CXX = g++
  # export MPICXX = mpicxx
  
  # the additional link flags you want to add
  ADD_LDFLAGS =
  
  # the additional compile flags you want to add
  ADD_CFLAGS =
  
  # Whether enable openmp support, needed for multi-threading.
  USE_OPENMP = 1
  
  # whether use HDFS support during compile
  USE_HDFS = 0
  
  # whether use AWS S3 support during compile
  USE_S3 = 0
  
  # whether use Azure blob support during compile
  USE_AZURE = 0
  
  # Rabit library version,
  # - librabit.a Normal distributed version.
  # - librabit_empty.a Non distributed mock version,
  LIB_RABIT = librabit.a
  
  # path to libjvm.so
  LIBJVM=$(JAVA_HOME)/jre/lib/amd64/server
  
  # List of additional plugins, checkout plugin folder.
  # uncomment the following lines to include these plugins
  # you can also add your own plugin like this
  #
  # XGB_PLUGINS += plugin/example/plugin.mk
  </code></pre>