The building commands used by ACLiC when you “+” code depend on the compiler options used when compiling ROOT itself. If ROOT was not built with --enable-cxx11, you need to add -std=c++11 to the command strings as you have done. However this is not enough, as you still get warnings.
Try also adding “-Wnoc++11-extensions” to the commands, like I did here: [C++11 in ROOT
The more durable method is to recompile ROOT itself with --enable-cxx11, since then the correct flags will be in the build commands automatically.
Jean-François