do you want to build cross-binutils (running on your host and linking or assembling for another target) or
do you want to cross-build binutils ( running on anather host )?
for cross-binutils try:
./configure --traget=i686-unknown-linux-gnu
(or powerpc-unknown-linux-gnu or ...)
for cross-building binutils try
export CC=name_crosscompiler_you_want_to use
before running configure
the crosstool.sh (
http://kegel.com/crosstool/) script is very helpful for building cross toolschains ;-)