Unable to compile KWidgetsAddons

[Nate Graham]

In trying to test out a KWidgetsAddons patch, I find that I'm unable to 
compile it on KDE Neon dev unstable the code due to a CMake error:
CMake Error in autotests/CMakeLists.txt:
  No known features for CXX compiler

  "GNU"

  version 5.4.0.

Full output available at https://paste.kde.org/piyy4wsnl


My g++ version looks okay:

$ g++ --version
g++ (Ubuntu 5.4.0-6ubuntu1~16.04.9) 5.4.0 20160609
Copyright (C) 2015 Free Software Foundation, Inc.


Nate