introduce getifaddrs for toolchains without it

David found that uclibc did not provide this slightly esoteric api
and provided one from BSD that can be built by the library internally.

AG: Made contingent on configure option --enable-builtin-getifaddrs

Signed-off-by: David <cymerio@gmail.com>
Signed-off-by: Andy Green <andy.green@linaro.org>
6 files changed