Don't show unused variable warnings/highlights for e.g. qScopeGuard

The following variable will be highlighted by Creator, presumably because it thinks it is unused:

auto panelSplitViewOpacityRollback = qScopeGuard([=](){ panelSplitView->setOpacity(1); });

This doesn't give a good impression of Creator's understanding of Qt API, as this is the intended usage of qScopeGuard:

https://doc.qt.io/qt-5/qscopeguard.html#qScopeGuard

Qt Creator 4.9.0
Based on Qt 5.12.2 (Clang 10.0 (Apple), 64 bit)
Built on Apr 11 2019 21:11:58
From revision 7885bc899f

The clang code model plugin is disabled.