Travis: adding clang to build configuration

.travis.yml

@@ -1,16 +1,30 @@
 language: cpp
+
+compiler:
+  - gcc
+  - clang
+
 before_install:
-  - sudo add-apt-repository -y ppa:ubuntu-toolchain-r/test
+  - echo $CXX
+  - if [ "$CXX" == "g++" ]; then sudo add-apt-repository -y ppa:ubuntu-toolchain-r/test; fi #gcc
+  - if [ "$CXX" == "clang++" ]; then sudo add-apt-repository -y ppa:h-rayflood/llvm; fi #clang
   - sudo apt-get update -qq
 install:
+  # VTK
   - sudo apt-get install -y libvtk5-dev libvtk5.8
-  - sudo apt-get install -qq gcc-4.8 g++-4.8
-  - sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-4.8 90
+  # gcc:
+  - if [ "$CXX" = "g++" ]; then sudo apt-get install -qq gcc-4.8 g++-4.8; fi
+  - if [ "$CXX" = "g++" ]; then sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-4.8 90; fi
+  - if [ "$CXX" = "g++" ]; then export CXX="g++-4.8"; fi
+  # clang:
+  - if [ "$CXX" == "clang++" ]; then sudo apt-get install --allow-unauthenticated -qq clang-3.4; fi
+  - if [ "$CXX" == "clang++" ]; then export CXXFLAGS=""; fi
+  - if [ "$CXX" == "clang++" ]; then export CXX="clang++-3.4"; fi
+  # OpenMP
   - sudo apt-get install -y openmpi-bin libopenmpi-dev
+  # ParMETIS
   - sudo apt-get install -y libparmetis-dev
-compiler:
-  - gcc
-# Change this to your needs
+
 env:
   - ENABLE_VTK=FALSE
   - ENABLE_VTK=TRUE