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.
Not sure if I asked before, but why is this needed on AIX? Also, what if a file is redirected as stdin, wouldn't we be reporting that it's a named pipe?