Add fs_fd to UV_PLATFORM_LOOP_FIELDS.
Include uv-aix.h on AIX.
Initial implementation of
void uv__platform_loop_init(uv_loop_t* loop)
void uv__platform_loop_delete(uv_loop_t* loop)
void uv__io_poll(uv_loop_t* loop, int timeout)
using pollset based on Linux epoll.
Add include/uv-private/uv-aix.h to sources.