Harmattan: Update instructions for C++11 builds with clang

Turns out that using C++11 with clang and STL from gcc 4.4 is not exactly
trivial. Here's the quick summary:

- The STL headers are broken (std::swap etc)
- The Qt headers are broken (user-defined string literals)
- Qt's moc is broken
c++11: use std::unique_ptr over std::auto_ptr which is deprecated