[cairo] OS X backend

[Keith Packard]

Around 14 o'clock on Dec 5, Carl Worth wrote:

> Finally, cairo is supposed to be able to work with X servers that
> don't have the Render extension, so some build improvements are still
> necessary to enable that case.

There's a difference between X servers not supporting the Render extension
and systems which use X but don't ship the Xrender library.  I'm not sure
we need to support the latter case at all.

-keith