lxqt-config-brightness: Use *_LDFLAGS in target_link_libraries
lxqt-config-brightness: Use *_LDFLAGS in target_link_libraries

stefonarch/lxqt-config,lxde/lxqt-config,lxde/lxqt-config,stefonarch/lxqt-config,lxde/lxqt-config,stefonarch/lxqt-config,lxde/lxqt-config