Ask Clang to use libstdc++ instead of libc++

Author: romainbrenguier

.travis.yml

@@ -29,7 +29,7 @@ matrix:
             - libc++-dev
       before_install:
         - sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/clang-3.7 90
-      env: COMPILER="clang++-3.7 -stdlib=libc++"
+      env: COMPILER="clang++-3.7 -stdlib=libstdc++"
     - os: osx
       compiler: gcc
       env: COMPILER=g++