export CFLAGS="-march=i486 -mtune=i686 -Os -pipe"
export CXXFLAGS="-march=i486 -mtune=i686 -Os -pipe"

binutils-2.19.1
---------------
$ mkdir ../build-binutils
$ cd ../build-binutils

../binutils-2.20/configure --prefix=/usr --enable-shared

time make tooldir=/usr
real    3m 44.31s

sudo make tooldir=/usr install

sudo cp ../binutils-2.20/include/libiberty.h /usr/include