qtbase: add PACKAGECONFIG for Link Time Optimization
qtbase: add PACKAGECONFIG for Link Time Optimization

qtbase configure option -ltcg enables Link Time Code Generation
using GCC's LTO feature. Enable it by default if the selected
optimization is for size.

Signed-off-by: Samuli Piippo <bc256dddab7848ac60359ced88151c0ee7641767@qt.io>

sapiippo/meta-qt5,meta-qt5/meta-qt5,schnitzeltony/meta-qt5,kraj/meta-qt5,sapiippo/meta-qt5,schnitzeltony/meta-qt5,meta-qt5/meta-qt5,kraj/meta-qt5