When a search path contains multiple "lib/" instances we previously
converted all or none. This fails for cases where only some of the
multiple instances must be converted. Teach AddArchitecturePaths to
generate all combinations that exist. Uncomment these cases in the
CMakeOnly.find_library test now that they work.
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.