On IBM i, getifaddrs is available renamed as Qp2getifaddrs; freeifaddrs
and struct ifaddr follow a similar fate. I assume this is in case AIX
decides to add it (as if). As such, just use the same implementation,
but rename the standard ones to the IBM i definitions and include its
header.
By usage of -fmodules, all the intrinsic items are loaded automatically.
The headers included come however from Visual Studio, thus bringing some
conflicting declarations. On the other hand, -fmodules is needed to
mitigate linking issues with clang in VS compatibility mode.
