Based on files languages/cpp/codegen/cppclasshelper.*
as removed by f31d32f49458897c97388a4b8f40f97e5af02f59
Needs "C++" added to values of X-KDevelop-Language for kdevclangsupport.json,
so kdevclang plugin is found when a "C++" language plugin is queried.
Needs someone with clue to complete whatever is done for the variables
passed via the "included_files" key.