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.
Is the `binutils --with-lib-path` patch sufficient to enable `gcc` to find the `crt*` object files? Or, is there some other way of adding `Formula['glibc'].lib` to `gcc`'s search path?