Update travis file for using libc++ with clang compiler

Author: Romain Brenguier

.travis.yml

@@ -32,19 +32,19 @@ matrix:
       before_install:
         - mkdir bin ; ln -s /usr/bin/clang-3.7 bin/gcc
       # env: COMPILER=clang++-3.7 SAN_FLAGS="-fsanitize=undefined -fno-sanitize-recover=undefined,integer -fno-omit-frame-pointer"
-      env: COMPILER=clang++-3.7
+      env: COMPILER="clang++-3.7 -stdlib=libc++"
     - os: osx
       compiler: gcc
       env: COMPILER=g++
     - os: osx
       compiler: clang
-      env: COMPILER=clang++
+      env: COMPILER="clang++ -stdlib=libc++"
     - env: NAME="CPP-LINT"
       script: scripts/run_lint.sh master HEAD || true
 
 script:
   - if [ -L bin/gcc ] ; then export PATH=$PWD/bin:$PATH ; fi ;
     make -C src minisat2-download &&
-    make -C src CXX=$COMPILER CXXFLAGS="-Wall -O2 -g -Werror -Wno-deprecated-register -pedantic -Wno-sign-compare" -j2 &&
+    make -C src CXX="$COMPILER" CXXFLAGS="-Wall -O2 -g -Werror -Wno-deprecated-register -pedantic -Wno-sign-compare" -j2 &&
     env UBSAN_OPTIONS=print_stacktrace=1 make -C regression test &&
-    make -C src CXX=$COMPILER CXXFLAGS=$FLAGS -j2 aa-symex.dir cegis.dir clobber.dir memory-models.dir musketeer.dir
+    make -C src CXX="$COMPILER" CXXFLAGS=$FLAGS -j2 aa-symex.dir cegis.dir clobber.dir memory-models.dir musketeer.dir