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``.
Add a "CMakeOnly.find_library" test covering various cases involving
lib->lib64 (non-)conversion. Comment out cases involving mixed path
components "lib" and "lib64", such as lib/A/lib64 and lib64/A/lib, as
these are known to be broken currently.