GCS: Need to run QMake if headers change

[tracernz]

To cause moc to run. Causes missing vtable at link time if Q_OBJECT is added to a class since qmake was last run (where the class previously had no virtual members). What about if classes are defined in cpp source...? Alternative is to build everywhere with clang and use the moc plugin for it.

[tracernz]

Or https://woboq.com/blog/verdigris-qt-without-moc.html