Fix CMake build types and compiler flags

Fix CMake build types and compiler flags

Turns out there were various typos in this that noone ever noticed,
most notably leading to QT_NO_DEBUG not being defined in RelWithDebInfo
builds. We're now also defaulting to RelWithDebInfo for Win32; please
let me know if that still causes problems.

While I was at it, I also added CMAKE_BUILD_TYPE=Profile, and pimped the
compiler warnings in general. In particular, -Woverloaded-virtual seems
rather useful with all the template trickery we're introducing lately.