On OS X Mountain Lion (10.8, released 2012) and later, ddd 3.4.0 installs a 0-byte ddd.1 manpage because:

sed -f ./unumlaut.sed ddd.man | cat > ddd.1~ \
            && mv ddd.1~ ddd.1
sed: 4: ./unumlaut.sed: RE error: illegal byte sequence

Both unumlaut.sed and ddd.man are in ISO-8859-1 encoding. sed on OS X 10.8 and later defaults to requiring its input to be UTF-8. If it is not, you need to tell sed what encoding it's in by setting LC_CTYPE as in the attached patch.

It would also be great if errors from sed were not silently ignored as they are now, due to the pipe. Piping to cat is a useless use of cat; removing it would fix the problem, though I understand that on some other platforms it does something other than cat here and so you may not want to remove it. But maybe there is some other way to satisfy that other platform that does not allow the build to proceed after an error has occurred.