Add a ``FIND_LIBRARY_USE_LIB32_PATHS`` global property analogous to the
``FIND_LIBRARY_USE_LIB64_PATHS`` property. This helps find commands on
multilib systems that use ``lib32`` directories and either do not have
``lib`` symlinks or point ``lib`` to ``lib64``.
The CMAKE_FRAMEWORK_PATH and CMAKE_APPBUNDLE_PATH cache variables are
supposed to be used to generate the extra paths passed to pkg-config,
but instead the CMAKE_PREFIX_PATH variable is used.
This bug was introduced by the refactor in commit v3.1.0-rc1~747^2~1.