Use CXX rather than CPP, ensure C++11 is enabled

Make sure that C++11 is enabled for all build types, use CXX rather than
CPP (as used by CMake).

Change-Id: I8ba7f835deae44516d92662104a7cc7c13281469
Merge topic 'cxx-flags' into master

511ae64a Use CXX rather than CPP, ensure C++11 is enabled