Waf has a utility function ('lib64' in waflib/Utils.py) which
either returns an empty string or '64' depending on if either of
the paths '/usr/lib64' or '/usr/local/lib64' exist. Then, the
build system itself decides its default LIBDIR to be either
/usr/lib or /usr/lib64 depending on the result of that function,
except when libdir is passed explicitly.
We don't allow lib64 in our packages. We do have the /usr/lib64
path as that is a symlink. Therefore, do not ever allow waf to
configure the path that way.