From Debian bug:

Matthias Klose wrote:
[....]
> > `debian/sauerbraten-dbg/usr/lib/debug//usr/lib/games/sauerbraten/sauer_cl
> >ient': Invalid operation dh_strip: objcopy returned exit code 1
> >
> > Is this a known problem with binutils-gold?
> 
> yes, I did see this as well recently.
Could it be that it is new with 2.20-3 or 2.20-4? I think I didn't saw that in
earlier version. I think I saw it the first time when compiling batctl - which
I compiled right after update of my Sources file. This was after the 11.
November.

I wanted to write a bug report right now but haven't a glue why it fails.

objcopy --only-keep-debug debian/batctl/usr/sbin/batctl debian/batctl-

seems to work without any problems. The real problem is 

objcopy --add-gnu-debuglink debian/batctl-dbg/usr/lib/debug//usr/sbin/batctl
debian/batctl/usr/sbin/batctl

So a small test would be:

$ echo 'int main() { return 0; }' > test.c && \
 gcc -g3 test.c -o test && \
 objcopy --only-keep-debug test test.dbg && \
 objcopy --add-gnu-debuglink=./test.dbg test && echo "cool it works"
objcopy:stCdJOm4: cannot create debug link section `./test.dbg': Invalid
operation

This works with the old linker, but not with binutils-gold

So I build the cvs version of the linker and objcopy and it is the same here. 
So it is propably an upstream bug.

Downstream bug can be found at http://bugs.debian.org/556951