building playandpaint example without building qt src causes error cannot find -lpnp_basictools

Building playandpaint example without building qt src causes the following line in the pro file to be interpreted incorrectly:
LIBS = -L$${QT_BUILD_TREE}/examples/widgets/tools/plugandpaint/plugins -lpnp_basictools
so the lib is not found because of not specifying correct path to it.