To be honest i'm surprised with the adoption of C++11, i know the toolchain supports C++11 since some time but still i can imagine there's lots of legacy code using C++03 or older.
C++11 compiler will compile C++03 code just fine, AFAIK.
There were a handful of breaking changes in C++11, but nothing that takes any meaningful amount of time to resolve. IME the only source of porting pain is libraries which conditionally use C++11 features where the C++03 and C++11 versions aren't semantically equivalent.