In single config mode extra compilers were not written to Visual
Studio project files, because they were not added to the fake project
object we're using to write a single config project.
Task-number: QTBUG-27505
Change-Id: Ie57b648861573496252f1383dc77e0729e244947
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>