lib64 symlink

[ryandesign]

Building 6.00.05 on macOS within MacPorts:

[100%] creating link from lib to lib64
cd /opt/local && ln -s -f -n lib lib64
ln: lib64: Operation not permitted
make[2]: *** [src/LNS] Error 1

("Operation not permitted" occurs because MacPorts protects /opt/local from unauthorized changes.)

There is never a lib64 directory on macOS; you shouldn't be trying to make one (nor a symlink of that name).

Even on non-Mac operating systems it seems like it is outside your program's purview to create a lib64 symlink within the installation prefix (which may also be used by other programs that may prefer, for example, for lib64 to be a separate directory rather than a symlink).