[cairo] build now works

[James Cloos]

I tried reverting fb0a40fc10849eb6e972be27c98685f6ab7bc344.  That
prevents the RenderChangePicture: BadValue error, but does not prevent
the X server lockup.

I did discover, though, that the lockup abates if the offending gecko is
kill(1)ed.

Allowing the XCB backend to use XRENDER's PDF blend ops, even with
everything Xorg at yesterday’s master, triggers BadValue errors.

And something in cairo’s acb surface deadlocks the X server.

-JimC
-- 
James Cloos <cloos at jhcloos.com>         OpenPGP: 1024D/ED7DAEA6