travis: Compile with C++11 support with cmake on clang.
travis: Compile with C++11 support with cmake on clang.

We can not add it to gcc yet, as gcc 4.6, as is used by the travis
server, does not support it yet.

KisImre/cpputest,bithium/cpputest,chenlianbing/cpputest,arstrube/cpputest,KisImre/cpputest,devMichaelJones/cpputest,Andne/cpputest,asgeroverby/cpputest,offa/cpputest,jaeguly/cpputest,Andne/cpputest,KisImre/cpputest,Mindtribe/cpputest,dawid-aurobit/cpputest,offa/cpputest,dawid-aurobit/cpputest,cpputest/cpputest,asgeroverby/cpputest,basvodde/cpputest,PaulBussmann/cpputest,Mindtribe/cpputest,arstrube/cpputest,asgeroverby/cpputest,offa/cpputest,cpputest/cpputest,jaeguly/cpputest,basvodde/cpputest,dawid-aurobit/cpputest,offa/cpputest,jaeguly/cpputest,devMichaelJones/cpputest,PaulBussmann/cpputest,maxilai/cpputest,chenlianbing/cpputest,Mindtribe/cpputest,dawid-aurobit/cpputest,PaulBussmann/cpputest,PaulBussmann/cpputest,cpputest/cpputest,bithium/cpputest,maxilai/cpputest,arstrube/cpputest,arstrube/cpputest,basvodde/cpputest,maxilai/cpputest,cpputest/cpputest,Andne/cpputest,jaeguly/cpputest,devMichaelJones/cpputest,asgeroverby/cpputest,KisImre/cpputest,bithium/cpputest,chenlianbing/cpputest,chenlianbing/cpputest,devMichaelJones/cpputest,basvodde/cpputest,bithium/cpputest,Mindtribe/cpputest,maxilai/cpputest,Andne/cpputest