gcc, binutils: link to Cellar instead of system libs

Symlinks `linuxbrew/lib` to Cellar for `gcc`, where `gcc` will automatically look because that is the prefix. Should fix the issue discussed recently in #107.
And another link: https://gitorious.org/guix/guix/commit/01d45404f69025c757c1800e8b64fdd29a8134a6
> distro: Configure ld and GCC to not look under /usr & co.
This fixes impurities with non-chroot builds on LFS-style distros.
* distro/packages/base.scm (binutils): Pass `--with-lib-path'. (gcc-4.7): Pass `--with-local-prefix'. * distro/packages/make-bootstrap.scm (%binutils-static): Pass `--with-lib-path'.