Provide the language option (e.g. "-x c++-header") when registering a
translation unit for the editor.
Task-number: QTCREATORBUG-14787
Change-Id: Ie06f9fdab302f1b21ba72cdb65b6aabf9f7bc04c
Reviewed-by: Erik Verbruggen <erik.verbruggen@theqtcompany.com>
