Use the new FindXKBCommon CMake module
Use the new FindXKBCommon CMake module

Closes #1381.
Use in conjunction with https://github.com/lxde/lxqt-build-tools/pull/23.

stefonarch/lxqt-panel,lxde/lxqt-panel,stefonarch/lxqt-panel,stefonarch/lxqt-panel,lxde/lxqt-panel