generate QGL header file from qgl.h

Task-number: QTBUG-16838
(backported from qtbase commit 8b8eebd8a41bd91aeb5b55b702a4dbc7a8db5752)
Change-Id: I4e79404fc8203c55bdbd09c6ae9c6c7cefa915b7
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>