find_library: Skip 'lib => lib<arch>' searches if one symlinks the other
The FIND_LIBRARY_USE_LIB32_PATHSand FIND_LIBRARY_USE_LIB64_PATHS global properties ask find_library to look in lib<arch>
directories automatically before corresponding lib
directories. However, if lib<arch>
is just a symlink to lib
(or vice-versa) then we should skip adding the lib<arch>
path.
This is important to avoid finding paths that are unnecessarily suffixed with <arch>
because the symlinks typically exist only to satisfy other software that expects them.