Restore Boost_LIBRARY_DIR* variables in PCL CMake configuration
Boost_LIBRARY_DIR_DEBUG
and Boost_LIBRARY_DIR_Release
variables should be automatically filled by CMake according to the BOOST_LIBRARYDIR
hint. That's why these variables ettings have been removed in 7b70763c.
For some reason, on Linux, PCL still finds and uses the system Boost, ignoring the BOOST_LIBRARYDIR
hint that is properly set. It already works as is on MacOS and Windows.
By directly setting these variables, we ensure using the correct superbuild Boost libs.
Edited by Nicolas Cadart