[rtems-net-legacy] Add getaddrinfo, gai_strerror and ipv6_addr

[chrisj at rtems.org]

Hi,

The move of the networking header files to the system headers means
the functionality exposed is all that can be provided. This breaks the
backward compatibility of the legacy stack. The solution is to add
what is needed when needed to the legacy stack.

This patch adds getaddrinfo, gai_strerror and ipv6_addr to the
legacy stack.

The getaddrinfo implementation is form a current FreeBSD and so 
is the test code.

There are a couple of housekeeping patches. One to move warnings
to a configure option and a fix for the generated headers 
dependency.

Chris