package/poke: enable uClibc-ng support

poke bundle gnulib that doesn't support the case where
host_os='linux-uclibc'. When cross-compiling, the guessed
answers are mostly wrong and gnulib will try to replace
snprintf with rpl_snprintf. This lead to "undefined reference
to `rpl_snprintf'" errors.

Signed-off-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>