aix: improve AIX compatibility for Node.js use

As we work through the changes to Node required to support
PowerPC platforms, we have had to introduce a changes to the
libuv component to support the AIX operating system.

These are the initial enabling changes required.
There are two commits related to this change.
* https://github.com/andrewlow/node/commit/1e742f3db7eb6f290133754de2da835fbd965e23
* https://github.com/andrewlow/node/commit/5e8ef30c8278411903a7def845688829c0c4b162

The first is an AIX work-around as it lacks socket introspection support for AF_UNIX sockets.
The second is specifically identifying 0,1,2 files as stdio pipes - then reporting them as UV_NAMED_PIPE - which is what you're pointing out.

In testing Node - this seemed to do the right thing for the tests. I can imagine scenarios where someone has closed stdout and then re-allocated that special numbered handle to point at something else. This would of course break the logic here, but we're already doing a best guess work-around. AIX simply doesn't support what we need.