[travis] xenial has clang by default.
[travis] xenial has clang by default.

root-mirror/root,root-mirror/root,karies/root,root-mirror/root,root-mirror/root,karies/root,olifre/root,olifre/root,karies/root,root-mirror/root,olifre/root,olifre/root,karies/root,root-mirror/root,karies/root,karies/root,olifre/root,olifre/root,olifre/root,root-mirror/root,karies/root,karies/root,olifre/root,karies/root,root-mirror/root,karies/root,olifre/root,karies/root,root-mirror/root,root-mirror/root,root-mirror/root,olifre/root,olifre/root