Libc++ renabled.

script/ci_build.sh

@@ -2,9 +2,9 @@
 
 set -ex
 
-#if [[ "${CXX}" == clang* ]]; then
-    #export CXXFLAGS="-stdlib=libc++"
-#fi
+if [[ "${CXX}" == clang* ]]; then
+    export CXXFLAGS="-stdlib=libc++"
+fi
 
 mkdir build && cd build