Add empty clangcpp parser functionality

The new parser is advertised in the help
An option is added to the command line argument
A new loadcpp function is added to parse with clang
No code needing clang library is added yet.

Change-Id: Iee07fce319e6be13d3689077ab61c1e4e44b5fc2
Reviewed-by: Kai Koehne <kai.koehne@qt.io>