FindQtWaylandScanner.cmake: Use qmake-query for HINT

Summary: Instead of hardcoded /usr/lib, same solution as in D9116

Test Plan: Works fine with kwayland 5.42.0.

Reviewers: Frameworks, Build System, cgiboudeaux

Reviewed By: cgiboudeaux

Tags: Frameworks, Build System

Differential Revision: https://phabricator.kde.org/D10201