Currently, section 9.1.1 relaxes the FHS requirement that /lib64 and
/usr/lib64 be used, but it doesn't prohibit installing files in that
location. However, due to the way Debian handles this (with symlinks),
bad things happen in terms of tracking files and conflicts if packages
install files into /lib64 and /usr/lib64 and rely on these symlinks.
I think we should instead prohibit (must not) installing files into
/lib64 and /usr/lib64 in packages with architecture amd64.