toolchain/helpers: make LFS mandatory for uclibc toolchains

As discussed on the mailing list drop the non-largefile option for
toolchains.
The size delta is minimal and it just complicates package dependencies.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>