libstdc++ != libc++

libstdc++ is gcc's C++ stdlib; libc++ is clang's (although clang can used libstdc++). libc++ supports all of C++11, although there's still some bugs. libc++ is ABI incompatible with libstdc++, but it's explicitly designed to support using both libstdc++ and libc++ within the same program, so that's often not a program.