Update the CMake cache to reflect current settings

During configuration some of the values for CMake properties (compiler flags etc.) may be changed either by the user (through command line parameters or option files), or by the configuration script itself (setting more aggressive options or detailed debugging for instance).

This change writes many of the relevant values back into the cache so they are available for introspection (using e.g. ccmake) or when the rerunning the configuration without specifying all options.